Johnston Reservoir at Clement Park is closed temporarily as a result of an outbreak of blue-green algae blooms.
The blue-green algae, also known as cyanobacteria, can produce toxins harmful to humans and animals. Signs have been posted warning against wading, fishing or contact with water in the lake, which has been closed since early August.
Colin Insley, director of parks, planning and construction for the Foothills Park and Recreation District, said the record heat in the area this summer likely led to the growth of the cyanobacteria.