State officials closed swimming at a lake in the San Bernardino Mountains because it had dangerous levels of algae.

The Department of Water Resources (DWR) issued a “warning” advisory for Silverwood Lake due to the presence of blue-green algae known as cyanobacteria.

“These are warnings that should be taken seriously,” said Doug Carlson from DWR. “People who ingest it or accidentally swallow these algae can become sick. Pets can die from it”

While the lake remained open to boating, the Sawpit and Cleghorn swim beaches were closed to swimming. Officials urged the public to avoid direct contact with visible algal blooms.

The recommendations are based on the potential health risks from blue-green algae. Water sampled in the Sawpit swim area contained approximately 6.1 micrograms of microcystins per liter (µg/L), a concentration just above the “Warning” action level of 6.0 µg/L.

Blue-green algae can pose health risks, particularly to children and pets. The toxic blue-green algae can cause eye irritation, allergic skin rash, mouth ulcers, vomiting, diarrhea, and cold and flu-like symptoms. Pets can be especially susceptible because they tend to drink while in the water and lick their fur afterwards.

The algal bloom can appear as blue-green, white or brown foam, scum or mats that can float on the water’s surface and accumulate along the shoreline and boat ramp area.

Algal blooms take place where there’s low circulation, agricultural runoff, warm water or a combination of these.

Bloom conditions can change rapidly, and wind and waves may move or concentrate the bloom into different regions of the lake, officials said.

The public is advised against eating shellfish or other fish that may be contaminated.

Castaic and Pyramid lakes have also been impacted by algal blooms this summer.