Cyanobacteria in Vermont

Icon with text stating "2019 Recruitment Flyer"Icon with text stating "2019 Monitor Training Schedule"Cyanobacteria (also known as blue-green algae) are common native organisms in lakes, ponds and rivers around the world.  In Vermont, they can be found in any water body, river or stream.  Some species of cyanobacteria produce toxins and these toxins have been documented in some Vermont lakes.  Cyanobacteria are not always toxic and it is not possible to tell by looking if toxins are present.  For this reason, the Vermont Department of Health and the Vermont DEC recommend that everyone avoid contact with cyanobacteria.

We can all safely swim, fish and boat in Vermont’s lakes and ponds if we learn to recognize cyanobacteria.  The information here will help you know when it is best to find another place for your family and pets to enjoy the water.

Play it safe!  Learn to recognize and avoid cyanobacteria.

To Report A Cyanobacteria (blue-green algae) Bloom*:

Use the Department of Health’s online form to report a bloom.  You may also send reports via email to Please include several photos – one or two close up and one or two farther away – and be able to identify the location on a map or provide detailed information about its’ location.

*Blooms are dense concentrations of cyanobacteria.  They often occur at the water surface and can cover large areas.  See the cyanobacteria conditions for examples.

Vermont uses 3 levels to describe cyanobacteria conditions:

  1. Generally Safe - Few if any cyanobacteria present.  The area should be safe for recreation. (See photos)
  2. Low Alert - Small amounts of cyanobacteria present.  The area is open for recreation, but caution is advised in any area where dense accumulations or scums are seen.  (See photos)
  3. High Alert - Large amounts of cyanobacteria are present and scums may occur in some areas.  The water is not safe for recreation. (See photos)

Screenshot of the cyanobacteria tracker - link to the cyanobacteria tracker           Microscopic view of algae - link to 'What you should know about cyanobacteria'            Water with algae - link to 'What you should do if you see a bloom'

Close up of algae bloom - link to 'What causes cyanobacteria blooms?'           Dog Fetching Stick in Water - link to factsheet for veterinarians            Leaves and water with algae - link to 'Learn More'


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