When the Charles, Mystic, and Neponset River Watershed Association (NepRWA) released its 2024 water quality report card grades for Boston’s urban rivers last month, the Neponset was assigned a B+ with a score of 82.3 percent, which indicates the water is almost always safe for swimming and boating.
According to the report, the improvements in the Neponset are a result of better stormwater treatment and a decrease in rainy weather.
NepRWA River Restoration Director Sean McCanty noted that “our report card is based on the last three years’ worth of water quality data and gives sites a score based on if it’s safe to swim (100 percent), only safe to boat (50 percent), or not safe enough for either (0 percent).:”
Since sampling is done monthly, not weekly or daily, it doesn’t reflect the level of safety on any specific day, he added.
“We have 41 sites getting six samples per year across three years, so the final grade is an average of these values. Higher scores like A’s and B’s mean it’s always safe for boating and usually safe for swimming, while lower scores mean it is sometimes safe for boating or unsafe for either activity.”
“The gradual improvement of the Neponset River and its tributaries is very gratifying to see,” said McCanty. “It’s a testament to the power of collaboration between the state and federal governments, who set stormwater standards; municipal partners who implement improvements like green infrastructure and conduct illicit discharge detection; and non-profits like NepRWA who monitor water quality and assist our towns with education and technical assistance on stormwater issues.”
This grading, however, does not consider other dangers, such as high flows and sharp rocks. It also does not incorporate the concerns about Polychlorinated Biphenyls (PCBs) at the Neponset Superfund site, which flows through Dorchester and Mattapan.
Though bacteria concentration has improved in all three rivers, each also continues to struggle with urban runoff, extreme weather, and aging sewer infrastructure.
“For most of our waterways, the biggest concern for swimming safety is the concern about the water making you sick,” McCanty said. “The best way we have to trace that is to test our water regularly for E. coli contamination. E. coli itself is usually not that high of a concern in terms of getting sick, but it comes from human and animal waste, which may carry other, more harmful bacteria.”
The Neponset Watershed has just one designated DCR-operated swimming site in Dorchester which is Tenean Beach, and “unfortunately,” McCanty said, “it is often unswimmable due to bacterial contamination.
“We’re working with DCR, the Boston Water and Sewer Commission, and Save the Harbor Save the Bay to find out the major causes of this contamination and get them resolved. We would love it if Dorchester residents were able to walk or bike along the Greenway trail and come to a lovely spot where they could jump in the water and enjoy the beach.”
