Toxic algae close Livermore’s Lake Del Valle to swimming

East Bay Regional Park District officials closed Livermore’s Lake Del Valle for swimming after discovering a toxic algae bloom in the the district’s largest lake, which provides drinking water for thousands in the Bay Area.

While filtration and treatment processes used after obtaining the water from the reservoir keep it safe to drink, the liquid’s toxicity exceeded the safety threshold set by the park district, said Carolyn Jones, a park district spokeswoman.

Park staff detected a bloom of blue-green algae Monday afternoon near the boat launch, and preliminary testing found the water’s toxicity exceeded the 20 parts per billion limit, Jones said. Samples will be sent to a laboratory in Florida for additional testing.

“People will still be drinking it, but it does call into question what is the acceptable threshold for drinking water,” Jones said, adding “there is no imminent threat to people’s health.”

Blue-green algae, also known as cyanobacteria, naturally form in surface waters. Clusters of the photosynthetic bacteria quickly multiply in warm, slow-moving, nutrient-rich water.