If Mill Brook in Arlington and Alewife Brook at the Arlington-Cambridge border were schoolchildren, they would be close to failing, water experts say.
Three associations concerned with watersheds that flow into the Boston Harbor, including Arlington’s Mystic River Watershed Association (MyRWA), this morning are announcing details of their annual water quality report grades in collaboration with the U.S. Environmental Protection Agency (USEPA).
The Mystic River watershed extends northwest as far as Reading and Wilmington. The river is made up of different water segments throughout several Middlesex County municpalities, including Mill and Alewife brooks. These two bodies of water were in the portion of the Mystic River scoring the lowest in this year’s water report; D+ and D, respectively, within an A+ though F grading spectrum. The full chart is below.
According to a news release from MyRWA, the letter grades are based on to what extent waterbodies meet bacteria standards for swimming and boating. These scores also weigh in factors such as river health, biodiversity of aquatic life, river flow, water temperature and other considerations. Dozens of volunteers collect water quality samples year round, which then are sent for analysis to the Massachusetts Water Resources Authority.
From 10 a.m. to 1 p.m Friday, Aug. 23, members of the USEPA, MyRWA, other Boston water associations and state and local leaders are to further discuss this year’s findings at 200 Rivers Edge Drive in Medford, along with describing efforts to restore water quality in urban rivers.
The pollution of Arlington’s segments of the Mystic River is becoming better known. Save the Alewife Brook is a local environmental organization started in 2021 dedicated to raising awareness about the untreated sewage dumped into Alewife Brook, at the town line between Arlington and Cambridge. According to the group’s website, the organization is especially concerned about Combined Sewer Outfalls (CSO), which discharge sewage water into the brook during major storm events, including several times earlier this year. 
According to the MyRWA statement, CSOs are the result of mid-19th-century water infrastructure built with a connected sewer and storm drain system. During very wet weather, especially when a lot of rain falls in a very short period of time, the amount of water coming through the system is more than the pipes can handle, and so it is designed to overflow, sending both the stormwater and the sewage into rivers and streams.
Alewife Brook in particular regularly receives the highest volume of untreated CSOs in all of greater Boston; according to the release, more than 200 million gallons of combined sewage were discharged into the Mystic River watershed in 2023 during at least 99 separate CSO discharges, such that Alewife Brook received more than 26 million gallons of untreated CSOs.
“Cities change rivers,” MyRWA Watershed Scientist Andy Hrycyna said in the release. “Every rainstorm brings untreated wastewater to rivers, streams and lakes, posing threats to the ecosystems and to our public health. The report card helps us see the impact of our built environment on our waterways and highlights the water bodies that are most affected. It’s a snapshot, and, we hope, a call to action.”
According to the release, 2023 was a “particularly wet year.” Last summer, heavy rains and flash floods caused intense damage across the state. MyRWA says that heavier rainfall patterns can exacerbate pollution, as stormwater sweeps pollutants like oil, gasoline, pet waste and trash off of roads, roofs and other surfaces directly into rivers, lakes and streams.
Read below for each water segment’s score, within the Mystic River watershed, for the Annual EPA Water Quality Report Card Grades:
| Water Segment | Grade |
| Upper Mystic Lake | A+ |
| Island End River | A – |
| Mystic River (salt water) | B+ |
| Chelsea River | B+ |
| Mystic River (fresh water) | B |
| Belle Isle Inlet | C+ |
| Meetinghouse Brook | C |
| Aberjona River | C- |
| Mill Brook | D + |
| Little River | D |
| Malden River | D |
| Alewife Brook | D |
| Winns Brook | D- |
| Mill Creek | F |
Feb. 12, 2024: Alewife Brook sewage bill moves forward
This news announcement was published Friday, Aug. 23, 2024, based on information from the Mystic River Water Association. It was prepared for publication by Brynn O’Connor, assistant to the editor.
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