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Potentially Harmful Algal Bloom on Charles River

August 14, 2015

The Cambridge Public Health Department recommends that people and pets avoid contact with a large, potentially harmful algal bloom that was detected on the Charles River last week.

On Aug. 13, state health officials notified the Cambridge Public Health Department that a water sample collected at Magazine Beach in Cambridge showed cyanobacteria (blue-green algae) concentrations roughly double the state’s guideline level.

“This state advisory is meant to be precautionary and does not mean that recreational activities in the Charles pose a high risk," said Sam Lipson, director of environmental health for the Cambridge Public Health Department. “The main concern is ingestion or swallowing of river water. We ask that people keep pets from drinking river water, and if people do get wet, they should rinse off.”

Some algal blooms can cause a range of ill health effects:
  • People who swallow or inhale small amounts of cyanobacteria can experience symptoms including gastroenteritis, nausea, vomiting, cramping, fever, and eye and mouth irritation.
  • People who swallow large amounts of blue-green algae can experience liver or neurological damage.
  • Inhaling water spray with algae in it can cause asthma-like symptoms.
  • Small children and pets are more susceptible to the effects of toxins than adults. Pet deaths from ingesting algal toxins have occurred.
These symptoms, both mild and severe, are associated with certain liver toxins and neurotoxins that are only present under certain conditions. The conditions favoring formation of toxins can change over time.

At this time, the most common liver toxin has not been detected in the algal bloom reported on Aug. 13, and will continue to be monitored. Past tests have not indicated significant amounts of the most common type of neurotoxin, but these tests are not routinely conducted.

The algal bloom reported on Aug. 13 is believed to extend from the Weld Boathouse near Harvard Square downstream to the Charles River Dam near the Museum of Science, according to the Charles River Watershed Association.

Algal blooms form in fresh water when cyanobacteria grow quickly and may form scums or mats in the water. These mats usually form in the between the Museum of Science and the BU Bridge (Charles River lower basin) and can move up river when the river flow is reduced during drought conditions. 

Some tips

  • People and pets should avoid touching or swallowing water with blue-green algae, and any shore areas where algae have washed up.
  • Dogs can get very ill and even die from licking algae off of their fur. Rinse dogs off immediately if they come into contact with an algae bloom.


For more information, call MDPH at 617-624-5757 or visit www.mass.gov/dph/environmental_health. You can also contact the Cambridge Public Health Department at 617-665-3838.


Suzy Feinberg, MPH
Public Information Officer

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