The city of Burlington closed two popular beaches Monday because of potentially toxic cyanobacteria in the water.
Swimmers were advised to stay out of the water at North Beach and the beach at Leddy Park because of the presence of cyanobacteria, commonly known as blue-green algae.
The bacteria can produce toxins harmful to humans and animals. Large blooms of the bacteria can also lead to major fish kills, as happened in Mississquoi Bay in 2012.
The Vermont Department of Health has volunteers along Lake Champlain and other troubled bodies of water who monitor for visual signs of cyanobacteria. According to those volunteers, the algae is present in St. Albans Bay and near Swanton.
State Toxicologist Sarah Vose said Monday that the state is in the process of testing water samples from the Burlington beaches for toxins that can affect the liver and nervous system.
"Not all blooms contain toxins inside their cells," she said. "Scientists don't really understand why some blooms make toxins inside their cells and other blooms don't."
Vose said Vermonters should avoid swimming in water with a visible green or blue-green scum. Pets can also become sick or die if exposed to the toxins.
Managed beach areas are all observed by health department volunteers who report algae sightings to the department, Vose said, and are generally safe to swim in if there aren't signs posted noting a beach closure.
The blooms are caused by an excess of phosphorus in the water, which is the subject of a new plan set to be released by the Environmental Protection Agency this summer. That plan will set targets for how much the state and its residents must reduce water pollution in order to stop overwhelming the lake's carrying capacity for phosphorus.
Vose said it's likely the bacterial blooms will continue in the coming weeks.
"We're just starting into our blue-green algae season, so as the weather stays warm and calm, we'll tend to see some blooms pop up in some spots," she said.
