The discovery of a blue-green algae in the water has Grant County warning people to avoid contact with Potholes Reservoir until further notice.
“The naturally forming bacteria often occur during hot weather and are extremely harmful to people and pets,” the Grant County Health District advised.
People are advised not to swim or water ski in the reservoir and keep all pets and livestock away.
Boaters should avoid all areas of scum, the health district said.
The same sort of advisory is in place for Moses Lake after testing last month also showed toxin levels above recreational guidelines.
Blue-green algae has also been confirmed in Willow Lake in Grant County but toxin levels were not shown to be above recreational guidelines.