The Neponset Watershed Association, Charles River Watershed Association, and Mystic River Watershed Association released their 2024 Water Quality Report Card on June 17, 2025.
Excerpts from the report follow:
“Since 2020, these watershed groups have assigned letter grades (A+ to F) to river segments based on how often water quality meets state bacteria standards for safe boating and swimming over the past three years. While all three rivers show continued improvement due to better stormwater management over the last few decades, all three still have lingering issues due to urban runoff, extreme weather, and aging sewer infrastructure. In particular, water bodies surrounded by paved or impervious surfaces experience worse water quality due to pet waste and other runoff entering waterways unfiltered…
The Charles, Mystic, and Neponset River Watershed Associations monitor water quality at more than 50 rivers, ponds, lakes, and estuaries. Grades are based on a three-year rolling average and factor in rainy versus dry weather to better reflect long-term trends and the impact of stormwater runoff. More than 150 trained volunteers collect and process samples every month. Samples are then analyzed by the Massachusetts Water Resources Authority (MWRA) laboratory at Deer Island, and the results are shared with the state through MassDEP’s external data submission program. This work has led to impairment listings and the development of remediation plans between the state and local municipalities…
The 2024 grades reflect a year marked by both heavy rain and a prolonged drought, which has only recently ended for most of the state. Intense storms can overwhelm sewer systems causing overflows into waterways and even homes. The Charles and Mystic still suffer from combined sewer overflows (CSOs)—a 19th-century design flaw that sends untreated sewage into rivers during heavy rains. While many cities have worked hard to reduce CSO events, they remain a serious health risk, especially in environmental justice communities. The Neponset has challenges with sewer underdrains, another type of older sewer infrastructure, and all three rivers still have some areas where cross connections between sewers and storm drains allow sewage to escape to the rivers…
CHARLES RIVER WATERSHED
In the Charles River, grades ranged from A’s in the upper and lower middle watersheds, B’s in the headwaters and Lower Basin, and a C+ in the Muddy River, following trends observed across recent years. More urbanized, paved areas consistently see lower grades due to stormwater pollution while greener, more forested areas of the watershed are safe for swimming on most days…
Three areas saw grades improve slightly –– the Lower Basin increased from a B- in 2023 to a B in 2024, and similar trends are seen in the Upper Middle Watershed and the Muddy River tributary. This improvement is a result of two drought years, which resulted in less stormwater runoff pollution, contributing to a slightly higher grade. The recent improvement in the Muddy River may be due to several years of restoration work, as well as improved watershed maintenance practices by local municipalities. However, Muddy River grades have fluctuated between a C+ and D- since 2004, which is significantly lower than the main stem of the Charles. A C+ grade still indicates highly degraded conditions, being safe for swimming only about 45% of the time. The Upper Watershed, Stop River tributary in Medfield, and Lower Middle Watershed maintained the same grades as last year.”
Map: Charles River Watershed Association
Read the full report.
