The Charles River downstream of the Longfellow Bridge is experiencing a bloom of blue-green algae called cyanobacteria that is harmful to humans, especially children and pets, the Massachusetts Department of Public Health said Thursday.
(Update on Oct. 9, 2024: The cyanobacteria bloom advisory in the Charles River downstream of the Longfellow Bridge was lifted Tuesday, according to the Charles River Watershed Association, after samples from Monday at Lechmere Canal, Broad Canal and Lederman Park showed cyanobacteria levels were below guideline of 70,000 cells per milliliter of water. In addition, the toxin microcystin was not detected.)
The state warns residents to stay away from the water and to rinse off skin that may have come into contact with the water. The algae can also release airborne toxins that can be particularly harmful to people with respiratory conditions such as asthma.
This is the first major bloom in four years, and one exacerbated by the “longest dry spell in 25 years, with no significant rainfall for more than three weeks,” according to the Charles River Watershed Association. A lack of water combined with heat and phosphorus from stormwater runoff create ideal conditions for toxic algae, which are naturally occurring microorganisms in rivers, lakes and ponds that can potentially release harmful cyanotoxins. The algae grow rapidly when bodies of water experience high phosphorus levels, hotter temperatures and stagnant conditions.
The state declares cyanobacteria a problem when the total cell count exceeds 70,000 cells per milliliter of water – and it is at about 93,000 cyanobacteria cells at spots in the Charles River, state health officials said.
Stormwater runoff is a significant problem for the Charles. This runoff comes primarily from large paved surfaces, primarily parking lots, where water cannot be absorbed into the ground naturally and it picks up harmful chemicals before flowing into drain pipes. Current regulations mandate a 50 percent reduction in runoff by 2038 in the Charles River Watershed, an area that includes 38 cities and towns in Eastern Massachusetts.
The federal Environmental Protection Agency announced in 2022 that certain large polluters would be required to comply with Clean Water Act permits to reduce pollution. The agency has yet to issue any of these permits, though, leading to a lawsuit by the watershed association and Conservation Law Foundation.
The EPA knows there is a problem, because it has a water quality buoy in the river outside of the Science Museum, foundation staff attorney Ameya Gehi said. “This toxic algae bloom is evidence of the ongoing unregulated stormwater pollution issues in the Charles River. Any more delay by the EPA risks more cyanobacteria blooms that threaten this communal treasure,” Gehi said. The case is on hold until the end of November.
The City of Cambridge has a Phosphorous Control Plan that seeks to achieve the first 25 percent of the city’s phosphorus load reduction requirement by June 30, 2028. New sewer deflection projects that would address runoff around Talbot Street, Binney Street and Western Avenue are expected to significantly reduce phosphorus. More details about this plan can be found on the city website.
If you see or smell a clogged catch basin near you, health officials advise residents to call the city’s Sewage Department at (617) 349-4861, because keeping catch basins clean helps prevent pollution from entering the water.
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