Health Advisory: Cyanobacteria Algae in the Charles River (Update)

Avoid Contact with Water Downstream of the River Street/Cambridge Street Bridge

The Cambridge Public Health Department is alerting residents of a cyanobacteria algae bloom in the Charles River downstream of the River Street/Cambridge Street bridge. (This includes Magazine Beach and the BU and MIT boathouses in addition to Broad Canal, Lechmere Canal, North Point Park, Lederman Park, the Community Boating docks, and Storrow Lagoon.) Residents are urged to exercise care in and near the water, particularly to prevent pets from drinking. Harmful algae blooms can be deadly for animals. Learn more about protecting pets.

The intent of this advisory is to make the public aware of the potential health risks of an algae bloom so that they can make informed decisions about whether to recreate on the Charles River. This includes swimming, fishing, boating, jet skiing, or engaging in other recreational activities on/in the water.

While this health advisory is in effect, individuals should not:   

•  Consume fish from this area 
•  Allow dogs to swim in or drink the water  

Algae and cyanobacteria (also called blue-green algae) are plant-like organisms that live in water. They can quickly grow out of control, or “bloom.” Some of these blooms produce neurotoxins (poisons) that make people and animals sick if ingested. If you, your child, or your pet comes in contact with the water, rinse off immediately. Contact can cause skin and eye irritation, and inhalation or ingestion can cause respiratory irritation and other illness.  If the blue-green algae are producing toxins, the health effects can be serious. More information about illnesses caused by harmful algal blooms can be found on the CDC website.

Contact a veterinarian immediately if your pet seems sick after going in or near water. Animals can get very sick or even die within hours of coming into contact with harmful algae or cyanobacteria. 

How long will this health advisory be in effect?   

This health advisory was first issued by the Massachusetts Department of Public Health (DPH) in late July, 2025. DPH has been monitoring cyanobacteria algae levels in this area and conducting sampling of the water for analysis. Since the first advisory was issued, the cyanobacteria bloom has expanded upstream. DPH will continue to monitor algae levels and advise communities along the river. The advisory will be lifted after two rounds of samples collected a week apart indicate that algae are no longer at levels that are considered unsafe.    

More information about harmful algal blooms can be found on the DPH website.