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The Charles River has been under a Massachusetts Department of Public Health advisory for a cyanobacterial bloom since August, but the advisory is expected to lift by the time thousands of rowers and spectators flock to Cambridge for the Head of the Charles rowing regatta this weekend.
The DPH conducted a water test on Oct. 8 that concluded the concentration of the bacteria had decreased to a safe level, according to Amanda J. Cox, spokesperson for the HOCR. Results from the latest test, which was performed on Tuesday, are expected to be released on Thursday — which would end the advisory if the results come back with safe levels of bacteria.
“With updated numbers, the advisory would only hold to the areas downstream of MIT, meaning the race course would be entirely below the DPH threshold,” Cox wrote.
Cyanobacteria produce toxins that can present serious health risks to the brain and liver when ingested, or asthma-like symptoms when water spray is inhaled. But even when an outbreak is present, the risk to rowers on the water is likely low.
Carl G. Zimba, president of the Charles River Alliance of Boaters, advises rowers to wash body parts that may be inadvertently exposed to the bacteria from splashes, but believes that the bigger concern is for pets that spectators may bring.
“Dogs will eat it and then suffer the consequences of cyanide exposure,” Zimba wrote.
“The main threat to people’s health that people have experienced is they ingest it,” Zimba said. “That’s where you get small mammals, dogs, children, who might eat some of it, and then they have a real problem.”
Cyanobacteria are present in all fresh water at low levels. Blooms, which often appear as a green tint in the water, are typically caused by excess nitrogen and phosphorus nutrients and warm temperatures.
This summer’s outbreak was first reported in the Charles River based on testing performed by the Charles River Watershed Association near MIT’s boathouse, less than one mile upstream of the Head of the Charles starting line. The July 31 report came after DPH staff alerted CRWA that the water looked abnormal.
Further testing revealed the cyanobacteria level far exceeded normal levels, prompting closures of some downstream areas and advisories to Cambridge residents to avoid contact with the water.
When health officials performed another round of testing on Oct. 2, they discovered the bloom had expanded further upstream, causing the advisory to be expanded from a stretch of river downstream of MIT to also include roughly half the distance between MIT and Harvard.
The Head of the Charles course runs three miles from Boston University’s DeWolfe Boathouse to Christian Herter Park, upstream of Harvard’s campus and the Eliot Bridge.
A similar advisory for cyanobacterial blooms in the Charles was put in effect in September 2024, lasting 19 days and ending before the annual regatta. That bloom was the first in more than three years.
“We’re in constant communication with the Department of Public Health, the DCR, as well as our athletes, volunteers, to ensure that everyone is up to date on the up-to-date information,” Cox said.
—Staff writer Shawn A. Boehmer can be reached at shawn.boehmer@thecrimson.com. Follow him on X @ShawnBoehmer.
—Staff writer Akshaya Ravi can be reached at akshaya.ravi@thecrimson.com. Follow her on X @akshayaravi22.
