The presence of blue-green algae prompted officials to close a popular beach on Lake Champlain in Burlington, Vermont.
North Beach was closed on Thursday. The Burlington Parks and Recreation Department also warned people not to allow dogs to swim in the water at Texaco Beach where the algae also has been spotted.
Blue-green algae or cyanobacteria can release a toxin that can sicken swimmers and pets.
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The toxic algae blooms that kill aquatic life and degrade the water quality on the lake have grown, fed by phosphorus-laden runoff of rain and snowmelt from farms, roads and parking lots and discharges from municipal wastewater treatment plants. The algae can multiply rapidly in warm conditions.