Cyanobacteria blooms begin annual reappearance in Vermont waterbodies

With summer in full swing, cyanobacteria blooms are occurring on more waterbodies and beaches across the state. Health officials want you to know what these potentially hazardous cyanobacteria blooms look like so you can avoid them.


Cyanobacteria are tiny microorganisms that are a natural part of freshwater ecosystems. Under certain conditions, cyanobacteria can multiply quickly, creating blooms on the water’s surface and wash up along shorelines. They can produce toxins harmful to humans and animals.

Swimming or wading in water with a cyanobacteria bloom may cause skin rashes, diarrhea, a sore throat, stomach problems, or more serious health concerns.

Blooms are usually green or blue-green and can make the water look like pea soup or spilled paint, but they can be other colors and consistencies too.

See a video and photos of what is — and isn’t — a cyanobacteria bloom.

“Take a quick scan of the water before you, your kids or your pets go in,” said Bridget O’Brien, a scientist with the Vermont Department of Health. “If you see any discolored water — or are unsure — play it safe and find another place to enjoy your outing.”

O’Brien said children can accidentally swallow the water when playing, and warned that blooms can be dangerous for pets, which may drink from the shoreline or swallow the cyanobacteria when licking water off their coats.

Vermonters can report cyanobacteria blooms using an online form that also allows for easy upload of photos. These reports are reviewed by staff from the health department, Lake Champlain Committee or Department of Environmental Conservation. Confirmed reports, along with location and any photos, are posted on the department’s Cyanobacteria Tracker.

The Cyanobacteria Tracker allows people to check conditions along Lake Champlain and various inland lakes in Vermont, as well as other recreational swimming areas.

Sites are identified as “generally safe,” “low alert” or “high alert.” The map shows where cyanobacteria blooms have been reported recently, but it can’t tell you what the conditions are currently at your favorite swimming area. Bloom conditions can and do change quickly, and not all locations are monitored. Vermonters should scan the water before going in, and always pay attention to any posted signs warning of blooms or beach closures.

If you think you see a cyanobacteria bloom:

  • Avoid contact with the water.
  • Do not let pets or livestock swim in or drink the water.
  • If you come in contact with cyanobacteria, rinse yourself off thoroughly as soon as possible. Talk with your health care provider if you have concerns from possible exposure.

Communities and others can access translated cyanobacteria information sheets and signs — “cyanobacteria alert” and “beach closed” — available in 12 languages.

For information about becoming a volunteer monitor, email the Lake Champlain Committee.

Learn more about cyanobacteria and what you can do at the department of health’s website, the department of environmental conservation’s website or the Lake Champlain Committee’s website.

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