Cyanobacteria (Blue-Green Algae)

Cyanobacteria, also known as blue-green algae, are naturally found in fresh water in the U.S. and in Lake Champlain and other Vermont waters. Some types of cyanobacteria can release natural toxins or poisons (called cyanotoxins) into the water, especially when they die and break down.

Cyanobacteria grow well in water that has high amounts of nutrients like phosphorous and nitrogen. Cyanobacteria can multiply quickly to form surface scums and dense populations known as blooms, especially during the warm days of late summer and early fall. In recent years, cyanobacteria blooms have occurred most often in northern sections of Lake Champlain—such as St. Albans Bay and Mississquoi Bay.

what do cyanobacteria look like?

It's important to know what cyanobacteria look like and to use your best judgment when thinking about swimming or doing other activities in the water. Watch the video below to find out. See more photos of what cyanobacteria look like and what are not cyanobacteria. And check weekly lake conditions.


To Report a Cyanobacteria (Blue-Green Algae) Bloom:
Email BloomAlert@vermont.gov with photos of the suspected bloom. If possible, include a detailed description of the bloom's location, or mark the bloom location using an image from an online mapping application such as Google, Bing or Yahoo Maps. Or you can call 800-439-8550 from 7:45 a.m. to 4:30 p.m. Monday through Friday (except state holidays).

health effects of exposure to cyanobacteria

Swimming or wading in water with cyanobacteria may cause minor skin rashes, sore throats, diarrhea, stomach problems, or more serious health problems. Children and pets are at higher risk of exposure because they are more likely to play near the shoreline and drink water while swimming. Pets can also lick and swallow cyanobacteria that may be caught in their fur.

The Health Department partners with other state agencies, environmental organizations, recreational site managers, town health officers, drinking water system operators and hundreds of volunteers to monitor cyanobacteria blooms each summer and test affected waters for cyanotoxins.

If you believe that someone has become sick because of exposure to cyanobacteria, get medical attention and call the Health Department at 800-439-8550.

Laboratory tests of water samples can confirm if a bloom is toxic. Learn more from the Vermont Watershed Management Division.

Download Cyanobacteria Fact Sheet
Check out the FAQs about cyanobacteria
Find out what veterinarians should know about animals and cyanobacteria

Guidance for Vermont Communities

Cyanobacteria blooms are expected to continue to increase in the coming years due to climate change and more nutrients—nitrogen and phosphorus—running off into waterways. Lakes and ponds previously not impacted by blooms may experience blooms. The Health Department offers a tool and reference guide for communities experiencing cyanobacteria blooms. This guide is intended for lakes and ponds with new or sporadic appearances of blooms. It is not appropriate for guidance in heavily impacted areas. This guide is not a regulatory guide, a prevention manual, nor a practice for public water system operation.
Download the Cyanobacteria Guidance for Vermont Communities

Vermont cyanobacteria (blue-green algae) tracker map

The Vermont Tracking portal brings together brings together environmental and public health data in one place to help Vermonters better understand the relationship between their environment and their health. Vermont Tracking also supplies data to the National Tracking Network to address local environmental public health concerns.

The Vermont Tracking portal includes a map of reported cyanobacteria blooms. The Cyanobacteria Tracker allows the public to check the recent cyanobacteria reports at shoreline sites and recreational swimming areas of Lake Champlain and various inland lakes in Vermont. At many sites, observations are made weekly from early June to early October. Sites are identified as "Generally Safe" or indicated as having cyanobacteria presence with "Low Alert" or "High Alert." 

VT Tracking logo
Check the Cyanobacteria Tracker Map


Cyanobacteria and Neurological Diseases

Amyotrophic lateral sclerosis (ALS), sometimes called Lou Gehrig's disease, is a devastating disease with no known cause. Only 5 to 10 percent of people with ALS have a family history (i.e. genetic cause) of the disease.

BMAA is an amino acid produced by some cyanobacteria. Researchers are testing the hypothesis of a link between BMAA exposure and ALS. This research is very preliminary and has not been proven. The Health Department will continue to review information as it becomes available.