The Clark County Public Health Department is warning swimmers to stay away from Vancouver Lake.

Toxic blue-green algae in the lake is at dangerous levels. It’s a health risk for people — especially small children — and could kill pets that drink the water.

Vancouver Lake Regional Park is still open.

Health officials say water sports at the lake are a bad idea, and people with motorized boats should avoid scum floating on the lake’s surface. Any fish caught at the lake should be cleaned well and organs should be discarded.

Blue-green algae, known to scientists as cyanobacteria, has been a growing concern in lakes and rivers across much of the U.S. in recent years. It has posed a risk to drinking water in Salem in the past, and led to advisories on the Willamette River in Portland.

Scientists link the spread of algae blooms to warm air and water temperatures.

Clark County officials plan to take weekly water samples at Vancouver Lake, and say they will update the county’s public beach website if conditions change.