BOSTON – The Boston Public Health Commission (BPHC) has issued an ongoing public health advisory regarding cyanobacteria in the Charles River.
As of October 8, 2025, the advisory now encompasses all areas downstream of the Cambridge Street bridge (commonly referred to as the River Street Bridge).
This expansion follows recent findings by the Massachusetts Department of Public Health (DPH), which identified elevated levels of cyanobacteria cells exceeding the state’s guidelines for recreational waterbodies.
The advisory initially began on August 1, 2025, when the BPHC alerted residents about a cyanobacteria algae bloom downstream of the Harvard Bridge.
Cyanobacteria, commonly known as blue-green algae, can produce toxins harmful to both people and pets, prompting authorities to advise residents to avoid contact with the water and any algae concentrations, even along the shoreline.
Activities such as swimming, fishing, paddleboarding, kayaking, and canoeing are discouraged.
Additionally, pet owners are warned against allowing dogs to swim in or drink the water from the Charles River.
Residents are encouraged to refer to the provided map at the bottom of the alert for exact locations where caution is advised.
In case of contact with the contaminated water, individuals are urged to rinse off immediately to reduce potential health risks.
Blue-green algae blooms can notably cloud the water, sometimes giving it the appearance of pea soup or paint, and present a significant health concern.
The primary risk for humans involves ingesting water containing these algae during recreational activities, while direct contact and inhalation of water droplets that may carry toxins pose secondary risks.
For dogs, the ingestion of water or algae scum can lead to severe health issues.
The health effects may vary from skin and eye irritation to serious gastrointestinal symptoms like vomiting and diarrhea.
Of particular concern are children and small pets, who may experience more severe effects due to their lower body weight.
These effects can include potential damage to the liver, kidneys, and neurological systems, with extreme cases leading to fatal outcomes.
Dog owners should remain vigilant for symptoms such as vomiting, staggering, drooling, or convulsions if their pets have been exposed to the algae bloom.
These symptoms typically emerge shortly after the dog’s interaction with the contaminated water or algae.
Reports of canine fatalities linked to the ingestion of harmful algae blooms have been noted in Massachusetts and across several other states.
Residents are left wondering when this advisory will be lifted, as algae blooms can persist for varying lengths of time, particularly in the summer months.
The Massachusetts Department of Public Health will maintain ongoing monitoring of the cyanobacteria levels in the affected areas.
Once the bloom subsides, laboratory sampling will be conducted.
The advisory can only be rescinded after two rounds of tests, conducted one week apart, show cyanobacteria levels below the threshold of 70,000 cells per milliliter of water.
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