Health Advisory: Officials Investigating Charles River for Cyanobacteria Algae Bloom

Avoid contact with Charles River's water between Kendrick Street in Needham and Spring Street in West Roxbury.

Tuesday, July 21, 2026 - The Boston Public Health Commission (BPHC) is alerting residents to a potential cyanobacteria algae bloom impacting the Charles River between Kendrick Street in Needham and Spring Street in West Roxbury. Impacted areas include Millennium Park and Cutler State Park. Massachusetts Department of Public Health (DPH) staff is awaiting test results to confirm the presence of cyanobacteria exceeding DPH guidelines for recreational waterbodies in Massachusetts. Cyanobacteria produce toxins that can make people and pets sick. Out of an abundance of caution, residents are urged to avoid contact with the water and any areas of algae concentration, even on shore.

People and pets should avoid contacting the waterway.

• Avoid direct contact with the water and impacted shoreline, including swimming and other water activities.

• Do not allow pets to swim in or drink the water.

See the map with precise location at the bottom of the release.

If you, your child, or your pet comes in contact with the water or algae on the shoreline, rinse off immediately.

Blue-green algae can form harmful blooms in lakes, ponds, and rivers that make the water murky, and can sometimes make the water look like pea soup or paint. Blue-green algae blooms can produce toxins that may make people and pets sick. Toxins may be present within the algae cells or in the water.

For humans, the primary concern is ingestion of water containing blue-green algae while swimming. Direct skin contact with the blue-green algae and inhalation of water droplets containing blue-green algae or toxins is a secondary concern. For pets, the primary concern is the ingestion of water containing blue-green algae or scum that has washed ashore or gotten onto their skin or fur.

Contact may cause skin and eye irritation, and inhalation can cause respiratory irritation and exacerbate pre-existing respiratory conditions. Ingestion can cause acute gastrointestinal symptoms, such as vomiting and diarrhea. If the blue-green algae are producing toxins, the health effects can be more serious, especially for children and small pets due to their smaller body weights. These health effects can include issues with the functioning of the liver, kidneys, and/or neurological systems. In severe cases toxins produced by blue-green algae can result in death.

Call your veterinarian immediately if your pet has been around an algae bloom and shows symptoms such as vomiting, staggering, drooling, or convulsions. These symptoms present themselves soon after exposure. Pets have been known to eat the scum that washes ashore and lick scum out of their fur. In Massachusetts and in many other states, canine deaths have been documented due to the ingestion of harmful algae.

When will this advisory be lifted?

Harmful algae blooms are most common in the summer months when warm sunny conditions promote algae growth. The website mass.gov/algae-blooms includes an updated list of all bodies of water with algae bloom advisories. Algae blooms may last for weeks in the summertime or may disappear quite quickly. The Massachusetts Department of Public Health (DPH) will continue to monitor cyanobacteria algae levels in this area. DPH will conduct sampling for laboratory analysis once the bloom has dissipated. DPH requires two rounds of samples collected a week apart that are below the threshold of 70,000 cells/milliliter of water to determine that the advisory can be lifted.

If you have any questions, concerns, or would like more information, please call the Boston Public Health Commission's Environmental and Occupational Health Division at .

• Published by: Boston Public Health Commission