All recreational activities have been suspended at Diamond Valley Lake near Hemet because of an algal bloom outbreak.

Boating, fishing and hiking won’t be allowed until further notice as officials monitor the water for cyanobacteria — also known as blue-green algae, Metropolitan Water District spokeswoman Rebecca Kimitch said Thursday, June 21.

The lake will be closed until at least Wednesday, June 27, she said.

Activities won’t be allowed at least through Sunday, June 24, and the lake is always closed Mondays and Tuesdays.

Diamond Valley Lake recreation suspended temporarily due to blue-green algae covering the lake. “This is a recreation issue, not a drinking water issue,” said Dr. Mic Stewart, MWD's water quality manager. Read more: https://t.co/qrvH1YP5sH pic.twitter.com/sjOiinySno — MWD of SoCal (@mwdh2o) June 22, 2018

“By next Wednesday we’ll be reassessing,” Kimitch said. “We’ll be testing all the time and make another determination.”

The bloom has turned the water green and is releasing cyanotoxins, which in high concentrations can be harmful to humans and animals, especially when ingested.

But the water district said there is no threat to the drinking water stored in the reservoir.

“This is a recreation issue, not a drinking water issue,” Mic Stewart, Metropolitan’swater quality manager, said in a news release. “We don’t want folks coming into contact with or fishing in this water.”

The district is not currently using the lake as a drinking-water source, Stewart said.

“Even if we did, our processes for withdrawing the water from the lake and treating it will ensure its safety,” he said.

The district, which runs the reservoir, began handing out fliers Friday, June 15, urging boaters to keep their children and service animals away from the water and not to touch or drink it. Swimming already is prohibited at the lake.

The cyanobacteria at the lake has been found at other Inland and Southern California lakes in the past. At various times in recent years, swimming has been shut down at Inland bodies of water such as Lake Elsinore, Canyon Lake, Silverwood Lake in San Bernardino County and others throughout the state.

The algae bloom, one the largest ever seen at Diamond Valley since it opened for recreation in October 2003, is caused by naturally occurring organisms that have produced large areas of green water and mats of green scum floating on the lake.

Blue-green algae blooms are common this time of year because of the warm weather as shallow waters are exposed to high external temperatures and light.

High temperatures in Hemet have reached at least 90 degrees on 14 days this month and have been above 80 degrees every day but two.

What lake-goers are seeing in the water is not traditional algae. Blue-green algae is a collection of bacteria, while green algae is more similar to a plant, Paul Rochelle, microbiology unit manager for the water district, has said.

Algae is typically found in open reservoirs during the summer. But knowing when it will disappear is harder to predict, district spokesman Bob Muir has said.

Diamond Valley Lake, Southern California’s largest drinking water reservoir, was built to store emergency water for the water district. It’s known as a haven for fishing and boating.

The lake was closed to private boats from April 2015 to May 2016, when the water level dropped because of the drought.