Kettletown State Park in Southbury is closed to swimmers after officials found blue-green algae in the water that can be toxic to people and dogs.
Officials with the Department of Energy and Environmental Protection announced the closure Tuesday afternoon and said they will run tests on the water to determine when it will be safe to reopen the beach.
Blue-green algae, or cyanobacteria, naturally occurs in Connecticut lakes and ponds and is usually harmless, but "nuisance blue-green algae blooms" can occur during extreme heat and when storm water runoff brings high levels of phosphorous into the water, according to the DEEP.
People exposed to a blue-green algae bloom can experience irritation of the skin, nose, eyes and respiratory tract; vomiting and diarrhea and problems with the liver or nervous system if large amounts of algae are ingested, the DEEP said.
More information on blue-green algae is available on the DEEP website, along with a complete list of water quality test resultts at state parks in Connecticut.