On Friday U.S. Army Corps of Engineers announced that Rufus Woods Lake has been closed to in-water activities — including swimming and water skiing — because of unsafe levels of algae toxin.

Humans and animals also shouldn’t drink the lake water, said the Army Corps, and all pets and livestock should be kept away from the lake shore until further notice.

State Department of Health scientists say the culprit is anatoxin-a, a naturally occurring nerve toxin produced by some blued-green algae blooms, which has been shown to be lethal to animals if ingested at high enough concentrations.

Last week, two separate water samples showed that the lake’s concentrations of the toxin surpassed state recommendations of one microgram per liter of water for recreational uses. Samples showed the lake contained six to 31 micrograms per liter.

Despite the warnings, Rufus Woods Lake remains open to the public and health officials say eating properly cleaned and gutted fish from the lake is safe but boaters are advised to avoid areas where algae blooms are present.