Lake Champlain cyanobacteria

Cyanobacteria blooms at Dog Beach in Burlington. 

BURLINGTON — Cyanobacteria blooms, an unwelcome staple of summer, have been forming in Vermont waters. These blooms can produce toxins that are harmful to humans and animals, and health officials want you to know what cyanobacteria blooms look like so you can avoid them while enjoying Vermont’s waters.

Cyanobacteria are tiny microorganisms that are a natural part of fresh water ecosystems. However, under certain conditions cyanobacteria can multiply quickly, creating scums and dense populations known as blooms on the water’s surface and along shorelines.

In recent years, blooms have occurred most often in northern sections of Lake Champlain, but are also found in other parts of Lake Champlain and other Vermont lakes. Some swim areas in Burlington have recently been closed due to blooms

Swimming or wading in water with a cyanobacteria bloom may cause skin rashes, diarrhea, a sore throat, stomach problems or more serious health concerns. Exposure is especially a concern for small children who may ingest the water while playing.

Cyanobacteria is also dangerous and potentially fatal to dogs, who may drink the water and lick the bloom residue off their fur.

Cyanobacteria 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. 

“By knowing what a bloom looks like, and scanning the water before you go in, you’ll know if you should stay out of the water,” said Bridget O’Brien, an environmental health scientist with the Vermont Department of Health. “Our state has so many great places to have fun in the water. Just stay informed, know what to look for, and you can find just the right places to swim and play safely.”

The Departments of Health and Environmental Conservation work closely with partners including the Lake Champlain Committee (LCC) to keep tabs on lakeshore conditions. Since 2003, LCC has trained community volunteers to monitor for cyanobacteria. These volunteer monitors, along with municipal recreational staff, as well as the Departments of Health and Environmental Conservation, provide data about where blooms are currently present.

In addition, Vermonters can help crowd source information of lake conditions. Using the online form at, people can send in reports of cyanobacteria blooms, relaying where a bloom is located, and easily upload photos as well. 

State officials and LCC staff review submitted reports, and post the information and photos at the Health Department’s Cyanobacteria Tracker. The Tracker map allows people to check conditions along Lake Champlain and other state waters. While the map shows where cyanobacteria blooms have been reported, bloom conditions can and do change quickly, so it is still important to check the water when you get there.

If you think you see a cyanobacteria bloom:

  • Avoid contact with the water. Especially keep small children away.

  • 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.

  • Report the bloom at

Cyanobacteria information, data and resources:

For more tips and information about staying healthy while enjoying summer in Vermont, visit

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