Stay Out Of The Charles River: Toxic Blue-Green Algae Bloom

WALTHAM, MA —The Charles River Watershed Association announced that on Wednesday they spotted a cyanobacteria bloom, also known as toxic blue-green algae, in sections of the Charles River in Waltham, Newton and Weston in addition to a section between the Mass Ave Bridge and the Longfellow Bridge in Boston and Cambridge.

The last confirmed bloom for the area was 2012.

"These cyanobacteria blooms are dangerous for human health, and animals such as dogs," Executive Director of The Charles River Watershed Association Emily Norton said in a statement. "Their appearance in the river every year is a reminder that our work restoring the Charles River is far from over."

The association said there is a bloom in the Lakes District, observed between Wares Cove and Fox Island.

Cyanobacteria blooms have also been fairly common in recent years in the Charles, prompting warnings to humans and pets. There were blooms reported in 2015, 2016, 2017, 2019 and this year. Phosphorus pollution that collect on roads and parking lots then drains into the water body and helps the blue-green sheets of algae grow.

Warmer weather and prolonged periods of dry weather followed by intense storms contribute to create perfect conditions for the cyanobacteria to grow, said officials. And it can take a while for the blooms to subside.

"These toxic algae blooms can be very persistent,” said Lisa Kumpf, Aquatic Scientist at the association. “Heat and sunlight, intense rainstorms that bring stormwater pollution, and low streamflow due to our current drought status, create the perfect environment for cyanobacteria to bloom. What’s worse: climate change predictions for the Northeast tell us this is only going to get worse if we do not address these issues now."

One part of the solution is to prevent polluted stormwater from entering the Charles River and other waterbodies, say experts. Green infrastructure like rain gardens can filter and clean stormwater before filtering it into the ground.

For general questions about cyanobacteria, contact the Massachusetts Department of Public Health: 617-624-5757 or visit mass.gov/dph/algae.