Know how cyanobacteria blooms look to keep family and pets safe

Wondering what’s floating in Vermont’s natural waters? Though the spring brought heavy pollen accumulation on some bodies of water, now is the time to be on the lookout for cyanobacteria, especially as you are looking to escape the heat.

With the official start of summer and warm weather, blooms of cyanobacteria (also known as blue-green algae) have begun to appear, and health officials want you to know what these potentially hazardous blooms look like so you can avoid them.

Photo by Vermont Department of Health. 
 Cyanobacteria can make dogs and humans sick or may even be fatal.
Photo by Vermont Department of Health.  Cyanobacteria can make dogs and humans sick or may even be fatal.

Cyanobacteria are tiny microorganisms that are a natural part of freshwater ecosystems. Under certain conditions, cyanobacteria can multiply quickly, create 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.

“Exposure to cyanobacteria can harm your health. It can be especially dangerous to children who accidentally swallow the water when playing, and for pets that may drink from the shoreline or swallow the cyanobacteria when licking water off their coats,” said Bridget O’Brien, an environmental health scientist with the Department of Health.

Know what a bloom looks like
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.

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

“It’s important to know what you are literally getting into,” said O’Brien. “Cyanobacteria blooms thrive in warm water, and as water temperatures rise, there will be more blooms showing up on lakes, ponds and beaches. If the water looks discolored, or even if you’re not sure if it’s a bloom — play it safe and find a different spot.”

The health department has a cyanobacteria tracker where people can check reported conditions along Lake Champlain and various inland lakes in Vermont. 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. Visit the website.

People can also report and upload photos of suspected cyanobacteria blooms using the Tracker’s online form. The reports are reviewed by experts from the Departments of Health and Environmental Conservation and the Lake Champlain Committee. Confirmed reports are posted on the cyanobacteria tracker.

Bloom conditions can and do change quickly, and not all locations are monitored. Vermonters should learn what blooms commonly look like, and always pay attention to any posted warning and closure signs. People can also check with their town for conditions at locally managed beaches.

If you think it’s 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 off thoroughly as soon as possible.
  • Talk with your health care provider if you have concerns about possible exposure.

Learn more about cyanobacteria and how to stay safe in the water:

The Lake Champlain Committee coordinates a program of volunteer cyanobacteria monitors. To get involved, email mail.