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Maine DEP Lake Scorecard

Middle Sandy River Pond

MIDAS Number: 3566

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The interactive scorecard image above summarizes many types of lake data into one color-coded graphic. The four main quadrants in the middle of the scorecard reflect the overall condition of the lake in four major categories: water quality trends, invasive plants, shoreland and habitat, and lake vulnerability.

The color is indicative of an overall condition assessment of each category: blue = Good, yellow = Fair, and red = Poor/At Risk. Each of the four major category assessments are based on scores of the sub-categories in the corresponding outer rim of the scorecard. Measurements that do not have enough data to make an assessment are displayed in grey (Table 1).

Hover over each section of the image to see a pop-up message that briefly explains why Middle Sandy River Pond scored a certain way. Click on any section to learn more about each parameter and how it was scored. Explore the links to the left for more information about each parameter, and why Middle Sandy River Pond scored the way it did for each category and sub-category.

Table 1: General scorecard condition descriptions for the four categories.

Condition Category	Water Quality Trends	Invasive Plants	Shoreland & Habitat	Lake Vulnerability
Good	Available data indicate that water quality is stable or improving	The lake may be at a reduced risk for a new aquatic invasive plant infestation	Shoreland and littoral habitat are likely only minimally impacted by shoreland activities	The lake may be less vulnerable to water quality changes than other lakes
Fair	Available data indicate that water quality may be declining	The lake may be at a moderate risk for a new aquatic invasive plant infestation	Shoreland and littoral habitat are likely moderately impacted by shoreland activities	The lake may be moderately vulnerable to water quality changes
Poor/At Risk	Available data indicate that water quality may be strongly declining	The lake may be at a higher risk for a new aquatic invasive plant infestation	Shoreland and littoral habitat are likely heavily impacted by shoreland activities	The lake may be highly vulnerable to water quality changes
Unknown	There isn’t enough information available to determine Water Quality Trends	There isn’t enough information to determine the threat of a new aquatic plant infestation due to lack of available data.	There isn’t enough information to determine the condition of the shoreland and littoral habitat due to lack of available data	There isn’t enough information to determine the vulnerability of the lake to water quality changes due to lack of data

For general information about Middle Sandy River Pond, click here.

The data and methods used to create the condition categories contained in the Maine DEP Lake Scorecard are explained below. If you have questions about the Scorecard, please contact us at this address: mainedeplakescorecard@maine.gov.

There are many ways that you can get involved to promote the health of Middle Sandy River Pond. See the Get Involved section for a list ways to take an active role in the condition of Middle Sandy River Pond.

Water Quality

Middle Sandy River Pond Water Quality: Results

Water Quality Trend Results

Long-term Secchi Disk Transparency (SDT), total phosphorus (TP), and Chlorophyll-a data are used to determine if the trophic state of a lake may be changing. Long-term trends may be calculated if there are at least 10 years of data collected within the last 30 years (1993-2022). These trend test results were used to inform the Water Quality Trends scores in the Maine Lake Scorecard. The results of trend tests are presented here if there have been enough data collected from Middle Sandy River Pond for any of these three parameters.

The Maine Department of Environmental Protection uses Mann-Kendall tau (τ) trend tests on these data to test for significantly changing conditions. The tau value is a measure of trend direction and magnitude. Positive tau values indicate positive (upward) trends, negative tau values indicate negative (downward) trends. Values further from zero (closer to -1 or 1) indicate a stronger trend. Tau values less than -0.5 or more than 0.5 here suggest the trophic state of a lake may be changing. Trends with p-values less than 0.05 indicate statistically significant trends.

It’s important to note that what is presented here represents trends in lake water quality data, not a measure of current condition. For example, a lake flagged in red for “Poor/At Risk” does not necessarily mean it is experiencing harmful algae blooms; it means that a declining trend in water quality is evident in the data record.

Click here to learn more about how the Maine Department of Environmental Protection uses trend test results to evaluate lakes as part of the Maine water quality standard review process.

To learn more about how Water Quality Trend data are collected and analyzed, click here.

There are not enough data to determine trends for Secchi disk transparency, total phosphorus, or chlorophyll for Middle Sandy River Pond. See the Get Involved section and the links below for more information on how you can help gather data to help determine the water quality condition and trends for Middle Sandy River Pond.

Algae Bloom Results

For the Algae Bloom subcategory, a minimum of 10 years of data is required to make an evaluation. If a lake has no algae blooms on record, the lake is scored as “Good”. If there is evidence that a lake has had occasional algae blooms (defined as blooms in less than half of the years with recorded data), the lake receives a “Fair” evaluation. If the lake has documented algae blooms for more than half of the years on record, it is placed in the “Poor/At Risk” category.

The occurrence of algae blooms is based on Secchi Disk Transparency (SDT) readings. If a SDT value is less than 2.0 meters, it is considered a bloom (although exceptions can occur). The data from Middle Sandy River Pond are represented in the plot below; any SDT readings indicative of an algae bloom will be above the green horizontal line at 2.0 meters and the points will be colored bright green. Note that the vertical axis in this plot is reversed, so that the top of the plot represents the surface of the lake.

To learn more about how Algae Bloom data are collected and analyzed, click here.

Middle Sandy River Pond does not have enough data (minimum 10 years) to determine the frequency of algae blooms.

Middle Sandy River Pond Water Quality: Total Score

Total score: The Water Quality Trend inner quadrant category is scored as an average of scores from the four sub-categories (Good = 1, Fair = 2, Poor/At Risk = 3; Table 2), as long as there is a minimum of two sub-categories with data. See the calculation for Middle Sandy River Pond in Table 3.

Table 2: Total Water Quality Category Scores

Overall Category Assessment	Average Score of sub-categories
Good	1
Fair	1-2
Poor	2-3
Unknown	Not enough data

Middle Sandy River Pond Water Quality Trend Score Calculation:

Table 3: Calculation for Middle Sandy River Pond Water Quality Trend metrics.

Parameter	score
Secchi Disk Transparency	Unknown
Total Phosphorus	Unknown
Chlorophyll-a	Unknown
Algae Blooms	Unknown
Average Water Quality Trend Score	Not Enough Data To Calculate Score

A Water Quality Trend score for Middle Sandy River Pond cannot be calculated at this time due to lack of data.

You can help strengthen these datasets and fill in gaps in the information we have for Middle Sandy River Pond. Start by clicking here for information on how you can help collect data, and see the Get Involved section to explore other opportunities to take an active role in the condition of Middle Sandy River Pond.

How Water Quality Scores were Calculated

Water Quality Trend Score Calculations

Water Quality Trend scores are based on changes in lake condition over time (TP = Total Phosphorus, Chl-a = Chlorophyll-a, SDT = Secchi Disk Transparency) or frequency of algae blooms. A Good (blue) designation indicates stable or improving water quality, Fair (yellow) indicates slightly declining conditions (or a stable trend but the values indicate high-nutrient conditions), and Poor/At Risk (red) indicates strongly declining water quality. The algae bloom score is Good (blue) for lakes that have never had a bloom observed, Fair (yellow) for occasional blooms, and Poor/At Risk (red) for frequent blooms.

Click here for more information about Water Quality Trends

There are four sub-categories within the Water Quality Trends quadrant of the Scorecard, each of which are used by the Maine DEP to evaluate lake condition in relation to the Maine Water Quality Standards for Lakes. Three of the sub-categories are based on trophic condition trends, or how lake biological productivity has been changing (or not) over time.

• TP (Total Phosphorus) is the primary nutrient needed for plant growth, especially algae in Maine lakes. It is generally present in small amounts in lakes and is usually what limits lake algae growth. As phosphorus concentration increases, generally the amount of algae in a lake also increases.

• Chl-a (Chlorophyll-a) is a measurement of the green pigment found in all plants including microscopic plants such as algae. Chlorophyll-a is used as an estimate of algal biomass in lakes; the higher the Chlorophyll-a value, the higher the concentration of algae in the lake.

• SDT (Secchi Disk Transparency) is a measure of the water clarity, or transparency, of the lake. Factors which reduce clarity are algae, zooplankton, water color, and silt. Since algae are generally the most abundant of these factors in Maine lakes, measuring transparency indirectly measures algal production.

• Algae Blooms are addressed in the fourth sub-category in the Water Quality Trends group. This metric evaluates the presence of in each lake. Algae blooms occur when algae grows so densely that water clarity, as measured by Secchi Disk Transparency, is less than 2 m (6.6 ft), indicating that excessive nutrients are present in the lake.

The Water Quality Trend sub-categories are scored as follows:

The Maine Department of Environmental Protection uses Mann-Kendall tau (τ) trend tests on these data to test for significantly changing conditions. The tau value is a measure of trend direction and magnitude. Positive tau values indicate positive (upward) trends, negative tau values indicate negative (downward) trends. Values further from zero (closer to -1 or 1) indicate a stronger trend. Tau values less than -0.5 or more than 0.5 here suggest the trophic state of a lake may be changing. Trends with p-values less than 0.05 indicate statistically significant trends.

For TP, Chl-a, and SDT: these trends are based on Mann-Kendall non-parametric trend tests. The trends are based on the most recent 30-year time period, and a minimum of 10 years of data is required to make an evaluation. This statistical test evaluates whether there is a pattern in the data over time that indicates changing conditions. The results of this test can be non-significant (p ≥ 0.05), indicating that the lake condition for the parameter under consideration is likely stable and not changing over time. If the result is significant (p < 0.05), the tau (τ) value is used to indicate the direction of the trend. Positive τ values indicate positive relationship, negative τ values indicate a negative relationship. The strength of the trend can also be evaluated with τ values; strongly positive trends approach τ = 1, while strongly negative trends approach τ = -1. Since changes over time are being evaluated, positive τ values indicate an increase in a measurement over time, and negative τ values indicate a decline in measured values over time. The methods for applying the scores in each scenario are detailed in Table 4.

Table 4: Scoring criteria for Water Quality Trends sub-categories: TP, Chl-a, and SDT.

Water Quality Trends	Assessment	Explanation
Good	Stable or variable water quality trend	Non-significant Mann-Kendall tests indicate stable water quality (or, in some cases, the data may be too variable to detect a trend). Significant results that reflect increasing water quality (negative tau for TP or Chl-a; positive tau for SDT) are also scored as GOOD.
Fair	Statistical decrease in water quality trend	If the Mann-Kendall trend test is found to be significant and tau is between 0 and 0.5 for TP or Chl-a (indicating an increase), or between -0.5 and 0 for SDT (indicating a decrease). OR If the water quality trend is stable, but the data indicate that nutrient conditions are elevated into the eutrophic range (more on this below).
Poor	Strong statistical decrease in water quality trend	If the Mann-Kendall test is significant and tau is between 0.5 and 1.0 for TP or Chl-a (indicating a strong increase), or between -1.0 and -0.5 for SDT (indicating a strong decrease)
Unknown	Parameter Unassessed	Not enough data are available to assess the water quality trend

 

There is an important caveat to the Water Quality Trend sub-category scoring; some lakes have a statistically stable trend but poor water quality. Lakes in this condition usually have high-nutrient (or “Eutrophic”) conditions, and the trend is stable because lake productivity is no longer limited by the availability of nutrients as it is in low-nutrient (“Oligotrophic”) or moderate-nutrient (“Mesotrophic”) lakes. Simply put, it’s not possible for lake water quality to continue to decline because conditions are already so diminished. Eutrophic lakes are usually in that condition because of human activity in the watershed, although some lakes can be naturally eutrophic. Lakes with stable trends and measurements indicating low- or moderate-nutrients are scored “Good” (blue) for SDT, TP, and Chl-a. Lakes with stable trends and over 75% of their yearly means for a specific measurement in the Eutrophic range are placed in the “Fair” (yellow) category for that measurement. Table 5 shows the ranges of these measurements that indicate nutrient status in Maine lakes.

Another factor that influences SDT is water color; lakes with color > 30 SPU (SPU = “Standard Platinum Units”; 30 SPU would be the color of weak tea) may have reduced transparency because of water color, not algae abundance. In these cases, it is best to use Chl-a as an indicator of trophic status if possible.

 

Table 5: Numerical guidelines for evaluating trophic conditions in Maine lakes. m = meters; ppb = parts per billion = μg/L. Values for Chlorophyll-a and total phosphorus are based on epilimnetic (top-layer) core samples.

Measurement	Oligotrophic (low nutrients)	Mesotrophic (moderate nutrients)	Eutrophic (high nutrients)
Secchi Disk Transparency	> 8 m	4 - 8 m	< 4 m
Chlorophyll-a	< 1.5 ppb	1.5 - 7 ppb	> 7 ppb
Total Phosphorus	< 4.5 ppb	4.5 - 20 ppb	> 20 ppb

Water Quality Trend results for Middle Sandy River Pond may be seen here.

Algae Bloom Score Calculations

For the Algae Bloom subcategory, a minimum of 10 years of data is required to make an evaluation. If a lake has no algae blooms on record (indicated by a Secchi Disk reading less than 2.0 m) in the last 30 years (1995-2024), the lake is scored as “Good”. If there is evidence that a lake has had occasional algae blooms (defined as blooms in less than half of the years with recorded data), the lake receives a “Fair” evaluation. If the lake has documented algae blooms for more than half of the years on record, it is placed in the “Poor/At Risk” category (Table 6).

Click here for more information about Algae Blooms

 

Table 6: Scoring criteria for Algae Blooms sub-category.

Algae Blooms	Assessment	Explanation
Good	No algae blooms on record	No instances of algae blooms on record (minimum 10 years of data)
Fair	Occasional algae blooms on record	Algae blooms have been documented in less than half of the years on record (minimum 10 years of data)
Poor	Frequent algae blooms on record	Algae blooms have been documented in more than half of the years on record (minimum 10 years of data)
Unknown	Parameter Unassessed	Not enough data are available to assess the prevalence of algae blooms

Algae Bloom results for Middle Sandy River Pond may be seen here.

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Shoreland & Habitat

Middle Sandy River Pond Shoreland & Habitat: Results

Shoreland Condition Results

Shoreland Condition - Lake shorelands help protect the lake from stormwater runoff and the pollutants it carries, and also support healthy shallow water habitat. Shoreland condition is adversely affected by the conversion of natural shoreland vegetation to human infrastructure such as buildings, roads, and lawns. Shoreland condition is scored here by measuring the percentage of impervious surface within a 500 m (0.3 mi) shoreland buffer area around the lake. Impervious surfaces include areas such as roads, driveways, and buildings increase stormwater runoff volume and energy by preventing water from soaking into the ground slowly. The scorecard categories are based on the amount of impervious surface in this shoreland area relative to lakes across Maine (blue = minimal development, yellow = intermediate, red = highly developed).

The results of the shoreland condition assessment for Middle Sandy River Pond are below. Figure 1 shows the results of this assessment, which places Middle Sandy River Pond in the Fair category. See the Shoreland Condition section for more details on this score. A map showing the amount of impervious surface in the Middle Sandy River Pond shoreland area is displayed in Figure 2.

Figure 1: Results of Shoreland Condition assessment. The Diamond represents the percentage of impervious surface area in the shoreland area around Middle Sandy River Pond in relation to all Maine lakes.

Figure 2: Map showing impervious surfaces in the 500 m (0.3 mi) shoreland area around Middle Sandy River Pond

To learn more about how Shoreland Condition data are collected and analyzed, click here.

Littoral Habitat Results

Littoral (shallow water) habitat assessments have not yet been conducted on Middle Sandy River Pond.

These surveys can be conducted by trained surveyors. Please contact the Lake Stewards of Maine if you’re interested in contracting for this service.

To learn more about how Littoral Habitat data are collected and analyzed, click here.

Middle Sandy River Pond Shoreland & Habitat: Total Score

Total score: The Shoreland & Habitat inner quadrant category is scored as an average of scores from the two sub-categories (Good = 1, Fair = 2, Poor/At Risk = 3; Table 7), as long as there is a minimum of one sub-category with data. The calculation for Middle Sandy River Pond is in Table 8.

Table 7: Total Shoreland & Habitat Scores.

Overall Category Assessment	Average Score of sub-categories
Good	1
Fair	1-2
Poor	2-3
Unknown	Not enough data

Middle Sandy River Pond Shoreland & Habitat Score Calculation:

Table 8: Calculation for Middle Sandy River Pond Shoreland & Habitat metrics.

Parameter	score
Littoral Habitat	Unknown
Shoreland Condition	2
Average Shoreland & Habitat Score	2

The average Shoreland & Habitat score for Middle Sandy River Pond is 2, which places it in the Fair category.

Good stewardship of a lake begins with a healthy shoreland area. There are many resources available to help protect and restore lake shorelands.

LakeSmart is a community-based lake protection program that educates shoreland homeowners about managing their property to protect water quality. Trained volunteers at more than 60 lakes in Maine lead LakeSmart visits with homeowners to identify and evaluate areas of runoff and erosion and recommend site-specific practices for keeping excess nutrients from reaching the lake. Middle Sandy River Pond is not currently active in the LakeSmart Program. For more information about LakeSmart, click here.

Resources about lake-friendly shoreland practices may be found on the Maine DEP Website. Regional Soil and Water Conservation Districts may also offer helpful resources for protecting lake shoreland areas.

A high amount of impervious surface in a lake shoreland area may be an indicator that the lake could benefit from a watershed survey and possibly some shoreland restoration practices. Grants and technical assistance are available to support such projects.

How Shoreland & Habitat Scores were Calculated

Shoreland Condition Score Calculations

Shoreland disturbance is the conversion of shorelands from natural vegetation to human infrastructure such as buildings, roads, and lawns. These activities have an adverse effect on the water quality and habitat condition of lakes. The amount of shoreland development was calculated here by measuring the percentage of impervious area within 500 meters (0.3 miles) of each lakeshore. Impervious surfaces include areas such as roads, driveways, houses that increase stormwater runoff volume and energy by preventing water from soaking into the ground slowly. The values were then compared for lakes across Maine; lakes with less 1% impervious surfaces in the 500 meter shoreland area were placed in the Good (minimal development) category, lakes with 1-10% impervious shoreland area were placed in the Intermediate development category, and lakes with greater than 10% impervious area were designated as Poor/At Risk. These thresholds were based on patterns observed in trophic conditions (phosphorus concentrations) in Maine lakes at varying levels of impervious shoreland area (Figure 3).

Click here for more information about Shoreland Condition

Impervious surfaces in the 500 m shoreland area of Maine lakes range from 0% to over 60%. However, most measurements for shoreland impervious area are quite low. 19.3 % of Lakes in Maine have no impervious surface at all in their 500 m shoreland area, and 62.1% of lakes have less than 1% impervious surface in this area (Figure 4). Despite these generally low amounts, impervious surface is an important metric for lake health because this particular type of land has an out-sized impact on water quality. When rain falls on impervious surfaces, it cannot soak into the ground and run into our waterways slowly; it runs off the land very fast. Due to this, impervious surface creates 16 times more stormwater runoff than forested land (Thomas, 1995). Impervious surfaces not only increase the amount of stormwater runoff, but these areas often contribute greater amounts of pollutants such nutrients, fertilizers, pesticides, herbicides, and vehicle fluids that accumulate on roads and parking areas. The increased energy of stormwater from impervious surfaces amplifies the erosive forces of runoff, destabilizing shorelands and transporting sediment and nutrients into lakes.

Impervious surfaces are easily picked up by satellite imagery due to their high reflectance. This makes them a good tool for measuring human activity near lakes at the watershed scale. The data used here were high-resolution (1 m, or 3.28 ft) C-CAP impervious cover data, captured in 2020 and 2021 and provided by the National Oceanic and Atmospheric Administration.

For this scorecard analysis, we set the condition category thresholds for impervious cover in the shoreland based on the relationship between impervious shoreland area and trophic condition across all lakes in Maine (Figure 3). The Trophic State Index (TSI) was first developed by Robert Carlson (1977) as a way to compare trophic condition (i.e., nutrient concentration, or biological productivity) across lakes and different trophic measurements. Total phosphorus was used as the trophic measure to calculate TSI here. TSI values can range from zero (extremely low nutrients and very little productivity) to 100 (extremely high nutrients and biological productivity). Change-points in TSI values were identified at 1% and 10% impervious shoreland area and were therefore used here as category threshold values (Figure 3). Maine lakes with less than 1% impervious surface in the shoreland area are generally have low biological productivity (TSI < 30). Lakes between 1% and 10% are most common to the moderately productive category (30 < TSI < 60). Lakes with shoreland impervious surface area greater than 10% are at the high end of the moderately productive category (TSI values close to 60).

Figure 3: Comparison of Trophic State Index (TSI) values across ranges of impervious surfaces in 500 meter shoreland areas across all Maine lakes, represented with boxplots that display the range of data within each case. The boxplot groupings (0-1%, 1-10%, and 10+%) indicate the thresholds used for Good, Fair, and Poor/At Risk category thresholds for Shoreland Habitat. The horizontal line across the middle of of each boxplot represents the median (center value) of the data, the top and bottom of the box represent the low (25th percentiles) and high (75th percentiles) values of the interquartile ranges, and the lines indicate the range of the data within 1.5 times the interquartile range. Points indicate outlying data points that are are not part of the normal expected distribution of the data.

Any lake that fell below 1% shoreland impervious area was placed in the “Good” category. Lakes that fell bewteen 1% and 10% shoreland impervious area were scored as “Fair”, and lakes with more than 10% impervious shoreland area were placed in the “Poor/At Risk” category. (Table 9).

A high amount of impervious surface in a lake shoreland area may be an indicator that the lake could benefit from a watershed survey and shoreland restoration practices. Grants and technical assistance are available to support such projects.

Figure 4: Distribution of percent impervious shoreland area amounts for all Maine lakes. The value for Middle Sandy River Pond is indicated by the red arrow at the bottom of the x-axis. The x-axis has been square-root transformed to better display the data as it skews towards zero.

References Cited:

Carlson, 1977. A Trophic State Index for Lakes. Limnology and Oceanography. 22:361-369.

Thomas, 1995. Environmental Land Planning Series: Site Planning for Urban Stream Protection. Prepared by the Metropolitan Washington Council of Governments and the Center for Watershed Protection, Silver Spring, Maryland.

Table 9: Scoring criteria for the Shoreland Disturbance sub-category.

Shoreland Condition	Assessment	Explanation
Good	Lake has minimal development in the shoreland area	The lake has less shoreland area development than 50% of the lakes in Maine
Fair	Lake has an intermediate level development in the shoreland area	The lake has more shoreland area development than 50% of lakes in Maine, but less than the most developed 25% of lakes
Poor	Lake has a high level of development in the shoreland area	The lake has more shoreland area development than 75% of the lakes in Maine
Unknown	Parameter Unassessed	Not enough data are available to assess the lake for shoreland disturbance

Shoreland Condition results for Middle Sandy River Pond may be seen here.

Littoral Habitat Score Calculations

Littoral habitat refers to the underwater features in the shallow parts of lakes and ponds that provide important cover, feeding areas, and breeding sites for all life found in lakes. Littoral habitat quality is diminished when the shoreland areas of lakes are converted from natural vegetation to human features such as lawns, buildings and roads.

The condition of Littoral Habitat is evaluated with field surveys that measure the quality of habitat compared to lakes with natural shorelines and no human development (blue = natural, yellow = intermediate, red = diminished habitat conditions).

Click here for more information about Littoral Habitat

Background - The National Lake Assessment is a survey of United States’ lakes that is coordinated by the Environmental Protection Agency. These surveys have found that shoreland disturbance – the conversion of lakeshores from natural vegetation to roads, homes, buildings, and other human-caused land alterations – is a major stressor to lakes, especially in the northeast United States. Lakes with high rates of shoreland disturbance have diminished habitat condition, in the nearshore terrestrial area as well as the shallow-water (littoral) area. Moreover, lakes with poor lakeshore habitat are three times as likely to be in generally poor biological condition.

Littoral Habitat work in Maine – The Maine DEP evaluates lakeshores to see if the habitat is in a natural condition, as the water quality standards for Maine lakes specify that lake habitat should be classified as “natural.”

These surveys are completed at 10 randomly-placed locations along the lakeshore. At each location, biologists record observational measurements about the presence of various forms of habitat structure in the littoral area, such as boulders and rocks of different sizes, fallen trees and branches, different types of plants, and overhanging vegetation from the shore. The presence and types of near-shore (“riparian”) vegetation are recorded, as well as any evidence of human activity on the shorefront (buildings, lawns, roads, etc.) Data from all 10 stations are combined in an analysis that places each lake into one of three categories of littoral habitat condition:

• Natural: the habitat is similar to that found in lakes with minimally-disturbed shorelands

• Intermediate: the habitat condition is likely being affected by shoreland disturbance; it is similar to that found in most lakes in Maine with some shoreland disturbance

• Diminished: the habitat is significantly different from that found in a natural condition; it is being greatly affected by shoreland disturbance

These three categories are directly translated here into three scoring levels for the Littoral Habitat sub-category (Table 10). To learn more about the Maine DEP littoral habitat surveys, please see this article (“Notes From the Shallows: Littorally Protecting Maine Lakes”), this technical paper (“Assessment indices of littoral habitat condition for lakes in Maine and New England, United States”), or this webinar recording.

 

Table 10: Scoring criteria for the Littoral Habitat sub-category.

Littoral Habitat	Assessment	Explanation
Good	Littoral habitat in natural condition	Data analyses from field surveys have determined that the littoral habitat is similar to that in lakes with natural habitat condition.
Fair	Littoral habitat in intermediate condition	Data analyses from field surveys have determined that the littoral habitat is similar to that in lakes with intermediate habitat condition.
Poor	Littoral habitat in diminished condition	Data analyses from field surveys have determined that the littoral habitat is similar to that in lakes with diminished habitat condition.
Unknown	Parameter Unassessed	Lake has not yet been assessed for littoral habitat condition.

Littoral Habitat results for Middle Sandy River Pond may be seen here.

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Lake Vulnerability

Lake vulnerability relates to how sensitive a lake is to various elements that influence the condition of its water. Sediment chemistry relates to how likely it is that phosphorus is released from the lake sediment; Runoff Pollution relates to elements of the watershed or lake that make the lake more susceptible to the effects of pollutants in stormwater runoff, and the Oxygen score indicates how likely it is that the lake will experience naturally low dissolved oxygen conditions, which may affect fish habitat and internal nutrient cycling.

In all three categories, blue = low vulnerability, yellow = moderate vulnerability, red = high vulnerability to water quality degradation. See the sections below for more information about each of these parameters.

Middle Sandy River Pond Vulnerability: Results

Sediment Chemistry Results

Sediment samples have not yet been collected from Middle Sandy River Pond for analysis of Al:Fe and Al:P ratios. Maine DEP is currently working with the state enviornmental lab to develop the capacity to run these samples in the future.

To learn more about how Sediment Chemistry data are collected and analyzed, click here.

Runoff Pollution Results

Middle Sandy River Pond has not been identified as especially vulnerable to Runoff Pollution at this time. By default, this places Middle Sandy River Pond in the Good category.

For more information about Nonpoint Source Pollution and Maine lakes, see the DEP Nonpoint Source Pollution webpage.

To learn more about how runoff pollution categories are determined and how they are used, click here.

Oxygen Results

The Oxygen score indicates how likely it is that the lake will experience naturally low dissolved oxygen conditions (anoxia), which may affect fish habitat and internal nutrient cycling. The results of the Oxygen model calculation for Middle Sandy River Pond are below.

As indicated in the plot, the likelihood of anoxic conditions decreases with increasing depth (horizonal x-axis), but simultaneously increases with a larger proportion of the lake underneath the epilimnion (curves going from blue to red).

The plot below shows the data for Middle Sandy River Pond (black diamond) as it relates to the predictive model for all lakes. The position of the diamond in the plot is a function of the maximum depth of the lake (horizontal x-axis) and the area below the epilimnion (the colored curved lines).The restuling vertical position of the diamond translates to the category results used in the Oxygen metric of the Scorecard: probability less than 0.25 (25%) of anoxia is Good, probability over 0.75 (75%) is At Risk, and probability between 0.25 - 0.75 is Fair.

The results below show that Middle Sandy River Pond is in the Fair category, meaning that the likelihood of extensive anoxia occurring naturally is moderate. If anoxia occurs here, it is possibly due to cultural factors. The lake is likely sensitive to cultural factors that influence anoxia.

Figure 5: Oxygen loss model results for Middle Sandy River Pond. See text above for a detailed explanation of this figure.

To learn more about how Oxygen modeling data are collected and analyzed, click here.

Middle Sandy River Pond Vulnerability: Total Score

Total score: The Lake Vulnerability inner quadrant category is scored as an average of scores from the three sub-categories (Good = 1, Fair = 2, Poor/At Risk = 3; Table 11), as long as there is a minimum of two sub-categories with data. See the Lake Vulnerability score calculation for Middle Sandy River Pond in Table 12.

Table 11: Total Lake Vulnerability Scores.

Overall Category Assessment	Average Score of sub-categories, rounded up
Good	1
Fair	2
Poor	3
Unknown	Not enough data

Middle Sandy River Pond Vulnerability Score Calculation:

Table 12: Calculation for Middle Sandy River Pond Vulnerability metrics.

Parameter	score
Sediment Chemistry	Unknown
Runoff Pollution	1
Oxygen	2
Average Lake Vulnerability Score	2

The average Lake Vulnerability score for Middle Sandy River Pond is 2, which places it in the Fair category. Middle Sandy River Pond is moderately vulnerable to water quality changes.

Understanding lake vulnerability is critical for making good decisions about how to best manage the multitude of factors that influence lake condition. Lakes that are especially sensitive to Non-Point Source (NPS) Pollution may quality for grant funds to be used for watershed plans and pollution mitigation installations. See the links below for more information about these opportunities.

• Watershed Assessments

• Nonpoint Source Pollution Priority Lake List

How Lake Vulnerability Scores were Calculated

Sediment Chemistry Score Calculations

Sediment chemistry indicates how likely it is that phosphorus (P) may be released from lake sediment under anoxic (low dissolved oxygen) conditions.

Click here for more information about Sediment Chemistry

In lakes, dissolved phosphorus (P) can bind to either aluminum (Al) or iron (Fe) compounds. Both Al and Fe can maintain this bond with P at the bottom of the lake as long as there is oxygen present. Iron, however, will change forms in anoxic conditions and release its bond with P. Al maintains its bond with P even under anoxic conditions. Therefore, the amounts of Al or Fe available in a lake to bind to P directly relate to the nutrient availability in most lakes in Maine. Internal release of P from lake sediment may influence the nutrient load of the lake enough to stimulate excessive growth of algae. Studies on Maine lakes¹ have shown that the ratios of Al to P and Al to Fe in the sediment provide a measurement to determine if the sediment will retain or release phosphorus into the water under anoxic conditions. If a lake has an Al to Fe ratio greater than 3:1 (three times as much Al as Fe) and an Al to P ratio greater than 25:1, the P will remain bound to sediment particles even under anoxic conditions. If these thresholds are not met, it is likely that P will be released from the sediment into the lake water if the water in contact with the sediment loses enough dissolved oxygen (less than 2.0 mg/L). The scoring of the Sediment Chemistry sub-category is based on lake sediment ratios of Al:Fe and Al:P (Table 13).

Table 13: Sediment Chemistry sub-category scoring criteria.

Sediment Chemistry	Assessment	Explanation
Good	Al:Fe > 3:1 AND Al:P > 25:1	Lake sediment meets both chemistry ratios that are favorable for retention of phosphorus in the sediment under anoxic conditions.
Fair	Al:Fe > 3:1 OR Al:P > 25:1	Lake sediment meets one of the chemistry ratios that are favorable for retention of phosphorus; phosphorus may be released from sediment under anoxic conditions
Poor	Al:Fe < 3:1 AND Al:P < 25:1	Lake sediment meets neither of the chemistry ratios that are favorable for retention of phosphorus; phosphorus is likely to be released from sediment under anoxic conditions
Unknown	Parameter Unassessed	Sediment chemistry has not been surveyed in this lake.

¹Below are some resources on the subject of lake sediment chemistry, with relevance to Maine lakes:

• Norton, S.A. What Role Do Soil and Sediment Play in Damping or Enhancing Eutrophication? Lake Stewards of Maine’s Water Column Newsletter, Winter 2022-2023, p. 21.

• Norton, S.A., Coolidge, K., Amirbahman, A., Bouchard, R., Kopáček, J. and Reinhardt, R., 2008. Speciation of Al, Fe, and P in recent sediment from three lakes in Maine, USA. Science of the total environment, 404(2-3), pp.276-283.

• Lake, B.A., Coolidge, K.M., Norton, S.A. and Amirbahman, A., 2007. Factors contributing to the internal loading of phosphorus from anoxic sediments in six Maine, USA, lakes. Science of the total Environment, 373(2-3), pp.534-541.

• Kopáček, J., Borovec, J., Hejzlar, J., Ulrich, K.U., Norton, S.A. and Amirbahman, A., 2005. Aluminum control of phosphorus sorption by lake sediments. Environmental science & technology, 39(22), pp.8784-8789.

Sediment Chemistry results for Middle Sandy River Pond may be seen here.

Runoff Pollution Score Calculations

The Runoff Pollution subcategory relates to elements of the lake or its watershed that make the lake more susceptible to the effects of pollutants in stormwater runoff.

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The catch-all phrase for these pollutants is nonpoint source pollution, or NPS. NPS is a term that is derived from the alternatively classified “point source pollution,” which is a term used to indicate pollution that comes from a single source, like a drainage pipe from a wastewater treatment plant. Most significant point-source pollution sources were eradicated from Maine lakes long ago, but NPS remains a significant threat to lake water quality in Maine. The Maine DEP maintains a list of “Priority” waterbodies that are especially threatened by or sensitive to NPS. Lakes may be on this Priority list for a variety of reasons, including if they:

• are on the Maine DEP’s 303d list of impaired waters
• are public water supplies
• support fish hatcheries
• show outstanding water quality
• are especially threatened by agricultural development
• have been recently designated as ‘impaired’ or near impairment
• show negative water clarity trends

Lakes were also included here as vulnerable to runoff pollution here if they have been have been designated as ‘impaired’ by pollution by Maine DEP, as noted in the Integrated Water Quality Monitoring and Assessment Report.

Unfavorable sediment chemistry ratios (indicating sediment release of P) can also be used to place lakes on the Priority list, but that component was not used here as it was used as its own subcategory, discussed above.

Lakes that are not public water supplies but have a significant portion of their watershed protected (either the land is conserved, or it is part of a watershed protection program) are not included in the Priority list because of reduced threats of watershed development. Additionally, lakes less than 50 acres are also generally not included on the Priority list since the development threat is not as great on smaller lakes; however, exceptions are made when there is a compelling reason to do so.

More information about NPS watershed pollution, and Maine DEP’s work to help reduce its effects on lakes, rivers, and streams, may be found here.

Lakes can be placed on the priority list for one or multiple reasons. Lakes on the list for multiple reasons were scored as “Poor/At Risk,” lakes with one reason were scored as “Fair,” and lakes not on the priority list were scored as “Good” (Table 14).

 

Table 14: Runoff Pollution subcategory scoring criteria.

Runoff Pollution	Assessment
Good	Lake not identified as especially vulnerable to NPS pollution
Fair	Lake listed as especially vulnerable to NPS pollution for one reason
Poor	Lake listed as especially vulnerable to NPS pollution for multiple reasons

Runoff Pollution results for Middle Sandy River Pond may be seen here.

Oxygen Score Calculations

The Oxygen score indicates how likely it is that the lake will experience naturally low dissolved oxygen (DO) conditions (anoxia), which may affect fish habitat and internal phosphorus cycling.

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Lakes often experience periods of low dissolved oxygen in the deep waters of the hypolimnion (the deepest layer of a stratified lake), as respiration from biological activity consumes oxygen faster than it may be replenished by photosynthesis or aeration from surface waters. This condition is exacerbated in lakes with unnaturally high amounts of decaying organic material, generally stemming from elevated phosphorus levels that stimulate excess algal growth. When these populations of algae cells die and sink to the bottom, there is increased bacterial respiration in the hypolimnion as the algal cells decay. However, some lakes experience low DO conditions in the hypolimnion despite having relatively low nutrient concentrations and low amounts of organic material and bacterial decay. These lakes may exhibit hypolimnetic anoxia simply due to the shape of the lake basin, which can contribute to stronger stratification and limit opportunities for replenishment of oxygen in deep waters during the open water season.

To determine which lakes may experience this ‘natural’ type of anoxia, Maine lake researchers developed a statistical tool¹ that predicts the likelihood that a lake will experience anoxic conditions based on basin morphometry alone. They did this by using DO profiles from low-nutrient lakes, where anoxia is unlikely to have a large effect on DO consumption, and checking for associations among various lake measurements like depth, size, and thermocline positioning. It was determined that the maximum depth of the lake and the percent of the lake area underneath the top layer of the stratified lake (the epilimnion) could accurately predict the percent likelihood of natural anoxia. In lakes where bathymetric data wasn’t available, maximum depth and the depth of the thermocline can be used to calculate the percent likelihood of natural anoxia. This anoxia model was used here in the Oxygen subcategory (Table 15).

Oxygen Glossary

• Anoxia: absence of dissolved oxygen in a lake; typically referred to when dissolved oxygen levels are less than 2.0 mg/L.

• Bathymetry: data that maps the bottom of a lake; comparable to topography for mountains, but the inverse.

• Epilimnion: In stratified lakes, the warmer top layer of the lake that generally remains oxygenated throughout the stratification period.

• Hypolimnion: In stratified lakes, the cooler bottom layer of the lake that may lose oxygen during the stratification period.

• Internal Phosphorus Cycling: the release of phosphorus from lake sediment that makes excess nutrients available for further algae growth in the lake.

• Lake Morphometry: related to the shape of the lake basin; deep, shallow, uneven, etc.

• Photosynthesis: The metabolic function of plants, including algae, that consumes carbon dioxide and produces oxygen. Photosynthesis is an important oxygenation mechanism in lakes.

• Thermocline: In stratified lakes, the depth at which the difference between warmer water above and cooler water below is greatest. Generally marks a transition zone in the lake’s water column.

 

Table 15: Oxygen subcategory scoring criteria.

Oxygen	Assessment	Explanation
Good	Less than 35% likely to experience natural hypolimnetic anoxia	Lake unlikely to have anoxia due only to basin morphometry
Fair	35-65% likelihood of natural anoxia	Lake may experience anoxia due only to basin morphometry
At Risk	Greater than 65% likelihood of natural anoxia	Lake likely to experience anoxia due to basin morphometry
Unknown	Parameter Unassessed	Data were not available to calculate model results for this lake

¹Deeds, J., Amirbahman, A., Norton, S.A., Suitor, D.G. and Bacon, L.C., 2021. Predicting anoxia in low‐nutrient temperate lakes. Ecological Applications, 31(6), p.e02361.

Oxygen model results for Middle Sandy River Pond may be seen here.

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Invasive Plants

Aquatic invasive plants are introduced exotic flora that displace native plant and animal communities. Infestations result in habitat disruption, loss of property values, diminished water quality, reduced fishing and water recreation opportunities, and significant expense for mitigating the environmental costs. Invasive aquatic species are evaluated in two categories here: Infestation Assessments and Risk Condition.

Middle Sandy River Pond Invasive Plants: Results

Infestation Assessment Results

Invasive plants have not yet been found in Middle Sandy River Pond, but it’s important to remember that survey efforts vary and infestations of aquatic invasive plants can go undetected for some time.

The best approach to keeping lakes free of aquatic invasive plants is frequent surveys and consistent preventative measures. See the Get Involved section for more information on aquatic invasive plant spread prevention.

To learn more about how the Infestation Assessment category was scored, click here.

View the Current Infestation map in a new browser tab by clicking here.

Risk Condition Results

There is a moderate risk of an aquatic invasive plant infestation in Middle Sandy River Pond. This determination was made through a risk-assessment model created by Maine DEP Aquatic Invasive Plant biologists. To learn more about how the Risk Condition category was scored, click here.

Learn more about the Maine Aquatic Invasive Plant vulnerability assessment model clicking here.

View an interactive vulnerability assessment map in a new browser tab by clicking here.

Middle Sandy River Pond Invasive Plants: Total Score

Total score: The Invasive Plants inner quadrant category is scored as an average of scores from the two sub-categories (Good = 1, Fair = 2, Poor/At Risk = 3; Table 16), as long as there is a minimum of one sub-category with data. See Invasive Plants total score calculation for Middle Sandy River Pond in Table 17.

Table 16: Total Invasive Plants Scores.

Overall Category Assessment	Average Score of sub-categories
Good	1
Fair	1-2
Poor	2-3
Unknown	Not enough data

Middle Sandy River Pond Invasive Plants Score Calculation:

Table 17: Calculation for Middle Sandy River Pond Invasive Plants metrics.

Parameter	score
Risk Condition	2
Infestation Assessment	1
Average Invasive Plants Score	1.5

The average Invasive Plants score for Middle Sandy River Pond is 1.5, which places it in the Fair category.

Prevention of infestation and early detection of any infestation is key to managing the spread of aquatic invasive plants in lakes. This is intensive work and is best conducted with many hands. See the links below for information about invasive aquatic plant management on your lake:

• Learn about Boat Inspections

• Establish a courtesy boat inspection program

• Seek funding for aquatic invasive plant prevention

• Learn about invasive aquatic plant identification and becoming a certified invasive plant patroller
  
  
  

How Invasive Plant Scores were Calculated

Infestation Assessment Score Calculations

The Infestation Assessment sub-category relates to the presence of invasive aquatic plants in a lake. If the lake has been surveyed within the last three years and no infestations have been observed or reported, the lake is listed in “Good” (blue) condition. If the lake was surveyed between three and six years ago and no infestations were observed or reported, the lake is scored as “Fair” (yellow) because it needs an updated survey for a proper assessment. If the lake has a current infestation of an invasive aquatic plant, the lake is scored in “Poor/At Risk” (red) condition (Table 18). An interactive map of current and eradicated aquatic invasive plant infestations is available here.

Table 18: Infestation Assessment sub-category scoring criteria.

Infestation Assessment	Assessment	Explanation
Good	Has been surveyed within last 3 years (2021 or later), no aquatic invasive plants found	Recent surveys (within the last three years) have found no infestations of aquatic invasive plants.
Fair	The lake was surveyed 3-6 years ago (2018-2020), no aquatic invasive plants were found	The lake was surveyed 3-6 years ago (2018-2020) and no aquatic invasive plants were found. New survey data are needed to make a better-informed determination.
Poor	Current known infestation	There is a current infestation of at least one species of invasive aquatic plant in this lake.
Unknown	There are old survey data only (before 2018) OR There are no survey data available	Either no data or only historic data are available; there is not enough information to make a determination on condition.

Infestation Assessment results for Middle Sandy River Pond may be seen here.

Risk Condition Score Calculations

Risk Condition is an indication of the likelihood of a new invasive aquatic plant infestation occurring at the lake. This is based on a risk-assessment model created by Maine DEP Invasive Aquatic Plant biologists. The vulnerability of a lake to novel invasive aquatic plant infestations is related to several key factors, including: volume of lake use, availability of public boat access, proximity to other infested waterbodies, potential for colonization, and others. More information on this analysis can be seen here.

Since all Maine lakes are at risk of an invasive aquatic plant infestation, there are no lakes in the “Good” (blue) category. Lakes are either put into categories of moderate risk (yellow) or elevated risk (red) (Table 19).

 

Table 19: AIS Risk Condition sub-category scoring criteria.

Risk Condition	Assessment	Explanation
Good	–	This category is not used: all Maine lakes are at risk for an invasive aquatic plant infestation.
Fair	Moderate Risk	There is a moderate risk of an invasive aquatic plant infestation.
Poor	High Risk	There is an elevated risk of an invasive aquatic plant infestation.
Unknown	Parameter Unassessed	Not enough data are available to assess the infestation risk for this lake.

Risk Condition results for Middle Sandy River Pond may be seen here.

Get Involved!

How You Can Help Your Lake

There are many ways for you to take an active role in the condition of Maine lakes. Supporting your local lake-focused organization is a great first step to getting involved. See the links below for specific ways to get involved that relate to the four components of lake health that are discussed here.

Water Quality – The collection of good monitoring data is essential to understanding the quality and condition of lakes. Volunteer lake monitors have an integral role in collecting these data. If you are interested in becoming a volunteer lake monitor, see the link below:

• Lake Stewards of Maine - Water Quality Monitoring

Invasive Plants – Prevention of infestation and early detection of any infestation is key to managing the spread of aquatic invasive plants in lakes. This is intensive work and is best conducted with many hands. See the links below for information about invasive aquatic plant management on your lake:

• Learn about Boat Inspections (Maine DEP)

• Establish a courtesy boat inspection program (a Maine DEP program administered by Lakes Environmental Association)

• Seek funding for aquatic invasive plant prevention (Maine DEP)

• Learn about invasive aquatic plant identification and becoming a certified invasive plant patroller (Lake Stewards of Maine)

Shoreland & Habitat – Good stewardship of your lake begins with a healthy shoreland area. There are programs in place to help establish and promote healthy lake shorelands which protect water quality and habitat.

• Manage non-point source pollution from shoreland development (Maine DEP)

• LakeSmart - to promote healthy lakeshores (Maine Lakes)

Lake Vulnerability – Understanding lake vulnerability is critical for making good decisions about how to best manage the multitude of factors that influence lake condition. Lakes that are especially sensitive to Non-Point Source (NPS) Pollution may quality for grant funds to be used for watershed plans and pollution mitigation installations. See the links below for more information about these opportunities.

• Watershed Assessments (Lake Stewards of Maine)

• Nonpoint Source Pollution Priority Lake List (Maine DEP)

Other ways to protect Maine lakes

• Join your Lake Association or start your own (Maine Lakes)

• Keep track of workshops, events, and other training opportunities workshops, events, and other training opportunities in Maine (Lake Stewards of Maine)

• Look out for loons! (Maine Lakes)

• Learn about all things Maine Lakes:

  • Maine Lakes Library (Maine Lakes)

  • Lake Stewards of Maine video library (Lake Stewards of Maine)

  • LakeSmart (Maine Lakes)

  • A field guide for things you’ll see in and near your lake (Lake Stewards of Maine)

  • A guide to science and stewardship of Maine Lakes (Maine Lakes)

  • Join the conversation about Maine Lakes (Maine Lakes)

  • Explore Maine Lake information (lakesofmaine.org, website managed by Lake Stewards of Maine)

  • Other ways to get involved (Lake Stewards of Maine)

Lake-Focused Organizations in Maine

Statewide:

• Lake Stewards of Maine

• Maine Lakes

• Maine Conservation Districts
  
  

Regional:

• Lakes Environmental Association

• 7 Lakes Alliance

• Midcoast Conservancy

• 30 Mile River Watershed Association

• Rangeley Lakes Heritage Trust

• Downeast Lakes Land Trust

• Kezar Lake Watershed Association
  
  

Watershed Districts:

• Portland Water District

• Cobbossee Water District

• York Water District

• Auburn Water District

Find a Lake Association

Click here to look for an active lake association in your area. If you don’t find one, consider starting one!

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