Despite steady improvement in water quality in recent years, increased rainfall and outdated infrastructure are hindering efforts to clean up the Mystic, Neponset and Charles Rivers, a coalition of watershed groups said Wednesday.
The watershed associations representing Boston's three major rivers released their annual water quality report cards, with grades for all three declining into the B's and C's over the course of 2025.
"These grades make it clear that progress has stalled," said Emily Norton, executive director of Charles River Watershed Association. "To achieve a truly clean, healthy, and swimmable Charles, we need to make the necessary investments in reducing stormwater runoff and ending sewage discharges."
The three associations have been assigning annual letter grades to their respective rivers since 2020 based on water quality testing and rainfall data. The report cards also include bacteria levels and what is considered safe for swimming and boating.
While the organizations' leaders acknowledged that steps are being taken to improve water quality, they pointed to aging infrastructure, including combined sewer systems, as impeding progress.
The effects of climate change, including increased rainfall and longer droughts are also impacting progress.
"When we talk about climate change, we often think about rising seas or an event that floods a river system," said State Rep. David Rogers, who attended the release of the ratings. "But we also must think about the urban infrastructure that was built years ago and frankly perhaps not with the changes we're experiencing in mind when they were first built."
More frequent heavy storms this past year lead to increased stormwater runoff, carrying unwanted nutrients directly into the rivers, according to the annual report cards. Longer periods of droughts are also causing warmer waters with limited flow.
In July 2025, a cyanobacteria bloom was reported in the Charles River, which lasted for 11 weeks — the second longest recorded bloom in the river's history.
Severe droughts in 2022, 2024 and 2025 also lowered the river's water levels. Within the past three years, roughly 16.6 million gallons of raw or untreated sewage was discharged into the Charles because of heavy rainfall.
Grades for the Neponset River, which is popular with hikers, swimmers and boaters, received predominately A and B grades.
Ian Cooke, head of the Neponset River Watershed Association, said the river has become "enormously cleaner" and more accessible, allowing communities to benefit from it.
"I think for the first time, we only have one out of 40 water quality stations that's not safe for boating essentially all the time," Cooke said. "That is an important milestone. We're not quite as far along in the swimming department, but we're making progress there too."
Grades for the Mystic River ranged from A to F with Upper Mystic Lake continuing to receive a perfect score. A tributary, Mill Creek in Chelsea, had the lowest with an F.
Some progress declined as a result of combined sewage overflows, like the Alewife Brook, which received a D.
"Protecting our rivers and streams is only possible if we know where the problems are," said Patrick Herron, executive director for Mystic River Watershed Association. "The next step is finding solutions, which we look forward to collaborating on with our wonderful partners in city, town, and state government."
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