Swimming, boating and fishing are prohibited in Lake Elsinore after water quality officials Friday detected harmful levels of toxins related to blue-green algae.
A notice on the city's website said the the popular recreation spot about 70 miles southeast of downtown Los Angeles would remain closed until further notice.
The notice said the Southern California Coastal Water Research Project informed the city Thursday night that the lake contains toxins exceeding recommended recreational health standards.
The most recent samples showed high concentrations of cylindrospermopsin, anatoxin-a and microsystins, all of which may cause harm to people, pets and livestock.
Exposure can cause rashes, skin or eye irritation, allergic reactions or gastrointestinal problems, and can be fatal to dogs, the notice said.
The water research project has been monitoring Lake Elsinore every other week because of the severe drought in Southern California and rapidly declining water levels.
The city and Elsinore Valley Municipal Water District add more than 5 million gallons of water a day to supplement natural flow into the lake. Despite the added water, the lake's level has fallen to its lowest since early 1993.
Algae blooms have also recently forced the closure of Pyramid Lake in Los Angeles County, Lake Temescal in Oakland and Discovery Bay in the Delta.