Lake Mead authorities are warning swimmers and watercraft users to stay out of algae-covered water at the Las Vegas Boat Harbor and near Hoover Dam.
The National Park Service said Friday that a bacterial toxin called microcystin has been detected in blue-green algae found in spots on the vast Colorado River reservoir that serves Las Vegas.
Officials say tests of similar algae spots downstream on Lake Mohave didn't test positive for microcystin.
Officials say the bacteria can cause skin irritation and gastrointestinal illness in humans and pets.
Southern Nevada Water Authority spokesman Bronson Mack says algae hasn't been seen near Las Vegas region drinking water intakes.
He says common treatment with ozone and chlorine would eliminate microcystin from water the authority supplies to homes and businesses.
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