Lake Massapoag Update: Summer 2025
It was a great summer on Lake Massapoag! Thanks to an alum treatment in June, residents and visitors enjoyed noticeably clearer water. Right after treatment, water clarity reached 13–15 feet, and while clarity decreased somewhat over the summer, it remained better than in recent years.
By the end of August, the Lake Massapoag Advisory Committee (LMAC) reported:
- Zero sightings of cyanobacteria (blue-green algae)
- Lower phosphorus levels, which help prevent harmful algae blooms
- Decreased levels of phycocyanin, a cyanobacteria marker
- Safe aluminum levels following the treatment — detectable in July (not a concern for swimming) and nondetectable by August
As a result, Veterans’ Memorial Park Beach, local camp beaches, and the Massapoag Yacht Club all stayed open the entire summer — a huge success, especially since more than 30 other beaches across Massachusetts had to close due to cyanobacteria or high E. coli levels.
Working together, with support from residents, partners, and municipal staff, Lake Massapoag is on a stronger path toward a clean, healthy, and resilient future.
- LMAC Water Quality Results: Town of Sharon – Lake Massapoag Advisory Committee
- More on Lake Massapoag: neponset.org/lake-massapoag
Lake Massapoag Watershed-Based Plan Update
This summer, the LMAC also made progress on its Lake Massapoag Watershed-Based Plan for the lake’s long-term health. The plan is being finalized with input from local partners, stakeholders, and contractors—including NepRWA.
Goals of the Lake Watershed Plan:
- Monitor lake water and inflowing streams for nutrients, bacteria, and cyanobacteria.
- Create a nutrient budget showing how much phosphorus comes from runoff, streams, and lake sediments.
- Identify “hot spots” to identify where pollution is highest.
- Model storm drain systems to target needed improvements.
- Recommend projects such as green infrastructure, stormwater retrofits, or in-lake treatments like alum.
- Combine science with community engagement through education, youth involvement, and local partnerships.
This year, NepRWA provided scientific expertise and data analysis to:
- Develop a phosphorus budget for the lake
- Conduct testing and feasibility studies
- Identify sites for future improvement projects to reduce pollution and protect water quality
For any questions about NepRWA’s work on Lake Massapoag, please email NepRWA Green Infrastructure Specialist, Anna Yie.
Funding from Mass EEA’s Municipal Vulnerability Preparedness Program, MassDEP’s 604(b) Watershed Planning Program, and Sharon’s Community Preservation Commission supported this work.
What is a Lake Watershed?
A lake watershed is the area of land that drains into a lake.
When it rains, water flows across streets, yards, forests, and wetlands, carrying with it soil, leaves, fertilizers, lawn chemicals, bacteria, and other pollutants.
All of that runoff eventually reaches the lake through streams, storm drains, or by soaking through the ground. Failing or poorly maintained septic systems can also leak into groundwater and harm the lake.
What happens in the lake watershed directly affects the lake’s water quality.
