If Mill Brook in Arlington and Alewife Brook on the Arlington-Cambridge border were schoolchildren, they would be on the verge of collapse, water experts say.

Three associations that manage the watersheds that flow into Boston Harbor, including the Mystic River Watershed Association (MyRWA) in Arlington, are releasing details of their annual water quality assessments this morning in collaboration with the U.S. Environmental Protection Agency (USEPA).

The Mystic River watershed extends northwest to Reading and Wilmington. The river is comprised of various watersheds in several Middlesex County communities, including Mill and Alewife Brooks. These two watersheds were in the portion of the Mystic River that received the lowest scores in this year’s water report; D+ and D, respectively, within a rating range of A+ to F. The full chart is provided toward the end of this report.

According to a press release from MyRWA, the grades are based on the extent to which water bodies meet bacteria standards for swimming and boating. These ratings also factor in factors such as river health, aquatic life diversity, river flow, water temperature and other aspects. Dozens of volunteers collect water quality samples throughout the year, which are then sent to the Massachusetts Water Resources Authority for analysis.

Today from 10 a.m. to 1 p.m., members of USEPA, MyRWA, other Boston water associations, and state and local leaders will further discuss this year’s results at 200 Rivers Edge Drive in Medford and describe efforts to restore water quality in urban rivers.

Pollution in Arlington’s sections of the Mystic River is becoming increasingly well known. Save the Alewife Brook is a local environmental organization founded in 2021 that aims to raise awareness about the untreated sewage being discharged into Alewife Brook on the Arlington-Cambridge city line. According to the group’s website, the organization is particularly concerned about the Combined Sewer Outfalls (CSO), which dump sewage into the creek during major storm events, including several times earlier this year. Map of the Mystic River watershed throughout Middlesex County and the ratings each watershed received. Photo courtesy: Mystic River Watershed Association. Below is a written report of each finding.

According to MyRWA’s statement, CSOs are the result of a mid-19th century water infrastructure that was built with a sewage and stormwater drainage system connected. In very wet weather, especially when a lot of rain falls in a very short period of time, the amount of water flowing through the system is greater than the pipes can handle, so the system is designed to overflow, discharging both the stormwater and sewage into rivers and streams.

In particular, Alewife Brook regularly receives the largest amount of untreated combined sewage in the entire Greater Boston area; according to the press release, in 2023, at least 99 separate CSO discharges discharged more than 200 million gallons of combined sewage into the Mystic River watershed, resulting in Alewife Brook receiving more than 26 million gallons of untreated combined sewage.

“Cities are changing rivers,” Andy Hrycyna, watershed scientist at MyRWA, said in the press release. “Every rainstorm brings raw sewage into rivers, streams and lakes, posing a threat to ecosystems and our public health. The report card helps us see the impacts of our built environment on our waterways and highlights the waters that are most impacted. It’s a snapshot in time and, we hope, a call to action.”

According to the press release, 2023 was a “particularly wet year.” Last summer, heavy rains and flash floods caused severe damage across the state. MyRWA says heavier rains can worsen pollution as stormwater washes pollutants such as oil, gasoline, animal droppings and garbage from roads, roofs and other surfaces directly into rivers, lakes and streams.

Below you will find a detailed list of the score of each water section in the Mystic River Basin for the Annual EPA Water Quality Report Card Grades:

February 12, 2024: Alewife Brook wastewater bill moves forward

This news release was issued on Friday, August 23, 2024, based on information provided by the Mystic River Water Association. It was prepared for publication by Brynn O’Connor, Assistant Editor.

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