Lake Elsinore - Photo courtesy of Marie1969 on Shutterstock

An algal bloom in Lake Elsinore prompted the state Friday to issue a “danger alert,” applying to all recreational activity, which officials said should be discontinued until further notice.

According to the California Water Resources Control Board, the bloom that appeared last week was confirmed to contain cyanobacteria, posing a potential health threat to people and pets.

“Cyanobacteria, a group of organisms that form harmful algal blooms, can produce potent toxins,” according to a Water Resources Control Board statement. “Health risks include skin inflammation, gastrointestinal distress, headaches, agitation and weakness or abnormal breathing if … material is swallowed while swimming.”

A “warning” was issued earlier this week, when the city posted “no swimming” signs along the shoreline. But due to the elevated risks, state and local officials believe that all forms of recreation should be suspended, including fishing and boating.

There was no timeline for a potential change in the alert status.

Officials said dogs shouldn’t be allowed to drink from the lake or eat scum that washes up on shore.

“Do not eat fish of shellfish from the water,” according to the WRCB. “Boiling or filtering will not make the water safe.”

Blooms have appeared in the lake in previous years, and according to officials, the current one is suspended at the surface.

Algal growth is attributed to higher volumes of nutrients in the water, combined with elevated temperatures, lots of sunshine and little to no wind.

“Bloom conditions can change rapidly, as the winds and waves move or concentrate the bloom into different regions of the lake,” the WRCB stated. “In some areas, the bloom may concentrate and form a film or scum on the water surface. The color of the water may also appear discolored as bright or dark green and brown.”

There have been no reports of medical emergencies connected with exposure to the green slime.

Additional information is available at

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