LOS ANGELES – State water managers are warning people to stay out of Castaic Lake due to a potentially dangerous algae bloom.

Lab tests this week found an increased level of toxins in the water due to the presence of blue-green algae, the California Department of Water Resources announced Tuesday.

People are urged to avoid swimming or recreating in the lake, avoid eating fish or shellfish from it, and avoid any contact with algal “scum” in the water or on shore.

“Boating is allowed, but water-contact recreation and sporting activities are not considered safe due to potential adverse health effects,” DWR said.

The warning covers the entire lake, with the exception of Castaic Lagoon. People are also urged to keep their pets and livestock out of the water.

While blue-green algae, or cyanobacteria, is a natural part of the lake’s ecosystem, levels can become elevated through warm water temperatures, storm runoff that carries nutrients – like fertilizer – into the water, and stagnation.

Exposure can cause rashes, eye irritation, vomiting, diarrhea and cold- or flu-like symptoms.

“Pets can be especially susceptible because they tend to drink while in the water and lick their fur afterward,” the agency said.

If you, someone you know or a pet has been exposed, experts recommend seeking medical help immediately.

The warning for Lake Castaic remains in effect until further notice.

Editor’s note: This article has been updated to correct the lake’s name.