Cyanobacteria, also known as blue-green algae, are a common and natural part of the microscopic plants (plankton) in Lake Champlain and other Vermont waters. Cyanobacteria can grow quickly during warm months in lakes and ponds with excess nutrients like phosphorus and nitrogen. Cyanobacteria blooms are most common on calm, sunny days between June and September. In recent years, cyanobacteria blooms have occurred most often in northern sections of Lake Champlain such as St. Albans Bay and Mississquoi Bay.
Intense precipitation events can increase nutrient inputs into water bodies, which, combined with warmer temperatures, may result in more favorable conditions for cyanobacterial blooms in Vermont’s lakes. As temperatures in Lake Champlain and other fresh water bodies continue to warm due to climate change, and the frequency of heavy precipitation events increases, conditions will become more favorable for blooms to happen.
Some types of cyanobacteria can release natural toxins or poisons (called cyanotoxins) into the water, especially when they die and break down. 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.
If the water is clear and the shoreline is free from green or brown scum, the water is probably safe to swim in. If there is a heavy scum on the water or shore, stay away from these areas until they are clear.
To Report a Cyanobacteria (Blue-Green Algae) Bloom:
Call: (800) 439-8550 7:45 a.m. to 4:30 p.m. Monday through Friday (except state holidays)
Email: AHS.VDHBlueGreenAlgae@vermont.gov after hours, weekends, and state holidays
You can include digital 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.
- Read the Lake Champlain Basin Program’s 2015 State of the Lake Report to learn more about the health of Lake Champlain and factors affecting cyanobacteria blooms
- Learn more about Vermont’s Clean Water Act (Act 64) passed in 2015 to help address water quality issues including excess nutrients in surface waters
- Smart WaterWays three-minute animated video—Chittenden County
- Make Some Waves—Lake Champlain Basin Program
- Get Involved—Lake Champlain Committee
- Low Impact Development Guide for Residential and Small Sites—Vermont Department of Environmental Conservation