Blog - Charles River Watershed Association

Cyanobacteria Outbreak in Lower Charles River

Posted by Alexandra Ash

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8/30/16 4:06 PM

Water samples collected last Thursday confirmed a cyanobacteria, or blue-green algae, outbreak in the Charles River Lower Basin downstream of the Massachusetts Avenue Bridge.


cyanobacteria bloom

Cyanobacteria bloom at Broad Canal in Cambridge

Concentrations of cyanobacteria exceeded 70,000 cells per milliliter of water, the water quality threshold established by the Massachusetts Department of Public Health. The monitoring buoy operated by U.S. EPA near the Museum of Science also recorded a spike in phycocyanin, an indirect measure of cyanobacteria, on Saturday. Public health officials recommend that people and pets avoid contact with the water in this area and rinse thoroughly in the event of contact.

When present in large numbers, cyanobacteria give the water a green, paint-like appearance and may produce toxins harmful to humans, dogs, and wildlife. Exposure to these toxins can cause eye, ear, and skin irritation. Emerging science shows a possible link to neurodegenerative diseases and a possibility of exposure by inhalation. Because cyanobacteria are most likely to release toxins as they die off, the health risks persist for about two weeks after cell counts decline to safe levels. In addition to the public health risk, by preventing light and oxygen from entering the water, cyanobacteria can smother fish and other aquatic organisms.


How can I reduce my risk during a cyanobacteria bloom?

  • Avoid contact with the water in areas effected by a cyanobacteria bloom.
  • In the event of contact with the water, rinse thoroughly.
  • Consider refraining from boating during the bloom or boat in a section of the river that is not affected.
  • Discourage your dog from swimming in or drinking the river water during a bloom.

LEARN MORE: Boating Safely on the Charles River


What causes cyanobacteria blooms?

The current bloom, the first documented this summer in the Lower Basin of the Charles, is part of an increasing trend as warmer summers and polluted stormwater provide ideal conditions for cyanobacteria to thrive. The Charles has experienced one or more cyanobacteria blooms in nine of the past eleven summers. The growth of cyanobacteria is fueled by phosphorus pollution accumulated on roads and parking lots, which is discharged into the Charles River via storm drains. An August 22nd rainstorm combined with the hot summer temperatures and the near record low flows in the river due to the extreme drought contributed to this outbreak.


According to U.S. EPA, the relationship between high phosphorus levels from stormwater discharges to the Charles River and the proliferation of cyanobacteria is well-established. Phosphorus is present in the Charles at more than twice the level the river can safely handle. However, there is a solution to this problem. Green infrastructure, such as rain gardens and constructed wetlands, filters polluted stormwater, reducing phosphorous pollution to the Charles River. 


What can I do to prevent cyanobacteria blooms?

  • Plant a rain garden on your property to filter stormwater and prevent it from entering the Charles River.
  • Replace impervious areas such as driveways and patios with permeable pavers or porous pavement.
  • Encourage your community to use green infrastructure to better manage polluted stormwater.
  • Avoid using fertilizer on your lawn or garden. If you do use fertilizer, make sure it is phosphorus-free.
  • Bring your car to a car wash that recycles water. This saves water too!

How can I help track cyanobacteria blooms?

Help CRWA and the Northeast Cyanobacteria Monitoring Program monitor cyanobacteria blooms in the rivers, streams and lakes near you. If you spot a portion of the Charles River or other waterbody that has turned the color of pea soup or looks like a blue-green paint spill, it may be a cyanobacteria bloom. With the new bloomWatch app, you can easily submit a picture and report the bloom.

Tracking and studying these blooms are the first step to keeping our communities safe. To get involved, find the bloomWatch app on Google PlayTM or on the App Store.

Get it on Google Play

Topics: Charles River, Stormwater, Stormwater Management, Pollution, Charles River Pollution, Stormwater Runoff

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About Charles River Watershed Association:

One of the country's oldest watershed organizations, Charles River Watershed Association (CRWA) was formed in 1965 in response to public concern about the declining condition of the Charles. Since its earliest days of advocacy, CRWA has figured prominently in major clean-up and watershed protection efforts, working with government officials and citizen groups from 35 Massachusetts watershed towns from Hopkinton to Boston. Initiatives over the last fifty years have dramatically improved the quality of water in the watershed and fundamentally changed approaches to water resource management.