Tracking Cyanobacteria (Blue-Green Algae) in Vermont

cyanobacteria

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. Some types of cyanobacteria can release natural toxins or poisons (called cyanotoxins) into the water, especially when they die and break down. 

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.

Since 2003, the Lake Champlain Committee (LCC) has trained citizen volunteers to monitor for cyanobacteria at lakeshore locations. Volunteer monitors, along with staff from the Vermont Departments of Health and Environmental Conservation, file weekly online reports that are then displayed on the Cyanobacteria Tracker Map. The program helps citizens, along with health, environmental and recreational officials, assess the safety of our beaches. It also provides important data to help us further understand when and why blooms occur.

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Explore the Cyanobateria Tracker Map


The Cyanobacteria Tracker Map is a data collaboration project of the Departments of Health and Environmental Conservation and the Lake Champlain Committee. The interactive map allows you to:

  • Vermont Cyanobacteria Tracker Tracking EPHT Check recent lake reports
  • Search by lake region, or by town
  • View the latest results by test site
  • Click on the site’s alert status for more information

Not all Vermont bays, lakes, and ponds are monitored. Be aware of changing conditions, and keep out of the water if you think cyanobacteria may be present.

NOTE: The map provides condition information and data as of the date of report. Test site observations and samples are collected once each week. Conditions can and do change. If you see cyanobacteria, don't go in the water.

Season Summaries: 2016 |2015 | 2014 | 2013 | 2012

Alert Levels

The color codes on the Cyanobacteria Tracker Map correspond with the following alert levels:

Green – Generally Safe
No toxic cyanobacteria blooms were found along these shoreline areas. These areas should be safe for recreational use.

Yellow – Low Alert
These shoreline areas have cyanobacteria at levels below bloom conditions. These areas are open for recreation, but caution is advised in any areas where dense accumulations or scums are seen.

Red – High Alert
These shorelines have cyanobacteria in dense scums at least in some areas. The water is not safe for recreational use in areas that contain scums.

Why do we have the Cyanobacteria (Blue-Green Algae) Tracker?

The Cyanobacteria (Blue-Green Algae) 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 most sites, observations are made once a week, from early June to mid-September. Sites are identified as “Generally Safe” or indicated as having cyanobacteria presence with “Low Alert” or “High Alert.”

While the map provides information on cyanobacteria conditions at the time of the report, lake conditions can change very quickly. It is important to learn to identify signs of a cyanobacteria bloom and use your best judgment when thinking about swimming or doing other activities in the water.

To check current conditions at your favorite beach or swimming area, you can call whoever is responsible for maintaining the beach. This may be the town, a private association, or Vermont State Parks.

Why is Cyanobacteria (Blue-Green Algae) a threat to public health?

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 Vermont Tracking Program was featured in the Centers for Disease Control and Prevention's Tracking in Action video series. See how the Cyanobacteria (Blue-Green Algae) Tracker helps residents make informed decisions about recreational lake use.