Water Quality Monitoring

30 Mile staff and volunteers annually monitor water quality on our lakes and ponds. We launched our program in 2016, monitoring six lakes, and have continued to grow the program each year. In 2023, we now monitor nine lakes on a bi-weekly schedule between May and October, and four small ponds three times each summer.

View water quality data collected on each lake & pond:

Why is water quality monitoring important?

Regular monitoring is a critical step in the development of baseline conditions. Without a strong baseline for any parameter, comparison of data within a single year, between years, or between lakes is not particularly helpful. Additionally, consistent and repeated data collection is essential in determining water quality trends. According to experts at Maine DEP, we need at least 10 years of baseline data before we will meet the minimum data threshold to complete statistical analyses that will identify water quality trends. Thus far, 30 Mile has completed 5 years of data for many of our lakes.

What do we monitor?

Water Clarity

Roughly every two weeks, we record water clarity (a.k.a. secchi disk transparency). This is a quick and simple method used to indirectly assess the concentration of algae in lakes. To measure water clarity, a black and white disk is lowered in the water and the reading is taken at the depth at which it is no longer visible. 

Dissolved Oxygen

Dissolved oxygen (DO) is a critical indicator of the health of the lake system. DO is produced through photosynthesis, consumed during respiration and decomposition, and is influenced by wind, wave action, weather events, and lake productivity. A good supply of oxygen is essential for fish and other aquatic species. As lakes become more biologically productive in the summer, oxygen can decline as decomposition occurs in deep areas of the lake. Loss of oxygen may indicate a stressed and changing ecosystem.  Understanding the pattern and extent of oxygen loss in deep areas is particularly important for lakes that may be more vulnerable for internal phosphorus loading due to unique sediment chemistry.

Phosphorus, Chlorophyll, and other parameters

Once per month, 30 Mile collects water samples and analyzes them for phosphorus and chlorophyll concentrations. Phosphorus is the nutrient that most influences the growth of algae in lakes. Phosphorus naturally occurs in soil, but is also found in fertilizers, septic systems, and animal or livestock waste, among other sources throughout a watershed. Chlorophyll is a pigment found in plants and algae. Measuring the concentration of this pigment helps us estimate the algal population in the lake. Once per season, a water quality sample is collected and analyzed for pH, Alkalinity, True Color, and Conductivity.

Where does the data go?

Near real-time data for all lakes in our monitoring program (secchi depth, dissolved oxygen and temperature) can be found by choosing a lake page above.

At the end of each season a comprehensive water quality annual report is generated for each lake summarizing the results, and updating historical data averages. 30 Mile staff and voluneteers are trained by Maine DEP, therefore our data is submitted and included with the statewide catalog of lake data, and is used to calculate state-wide trends, inform climate models, and in other lake-related research.

Additional Resources

Interested in becoming a volunteer water quality monitor?

Visit the Lake Steward’s of Maine training & certifications webpage to find out more, or contact Whitney Baker, 30 Mile’s Water Quality Program Coordinator at whitney@30mileriver.org.