Lake Anza is expected to re-open for swimming in April, now that the algae is gone. Photo: Josh S. Jackson

Recent rains have cleared toxic algae from several East Bay lakes, including Tilden’s Lake Anza, East Bay Regional Park District officials have announced.

That means, unless the algae returns, some popular swimming spots will re-open come April.

“Thanks to heavy rains from El Niño, toxic blue-green algae has cleared from Quarry Lakes in Fremont, Lake Temescal in Oakland and Lake Anza in Berkeley,” park officials announced Thursday. “These popular swim destinations were all closed … due to toxic algae blooms, and we’re thrilled to report that the algae has cleared.”

Lake Anza in Tilden Regional Park closed in September, following the earlier closures of Quarry and Temescal lakes. Carolyn Jones, park district spokeswoman, said the lakes first tested clear for the algae about a month ago, in December, but workers continued to test the waters to make sure no toxins were present.

“They’ve been super cautious,” she said. “Let’s hope that this is it for the algae.”

Swimming for humans isn’t slated to resume until April, but dogs should now be all right to swim in the lakes. Blue-green algae can be fatal for dogs, so that has been a particular concern since it appeared. Three dogs died last year after drinking from Lake Chabot, where the algae had cropped up.

Toxic algae can be highly visible, or not visible at all. In the photo above, algae can be seen at Lake Anza on Sept. 17. Photo: Sunshine Townsend/East Bay Regional Park District

Jones said scientists believe the drought and climate play a role in the proliferation of the algae, but that many unanswered questions remain.

“There are many mysteries with the algae all over the country,” she said. “No one is really quite sure what’s causing it. It’s probably climate related somehow, but what that is no one really seems to know. There are lots of theories.”

The park district did treat Lake Temescal with chemicals to try to clear the algae, but it wasn’t entirely effective. Park staff also cleared a blocked drainage pipe there so water could circulate better. The rains and colder temperatures that began in December appear, for now, to have done the trick.

Park officials will continue to test the water on a weekly basis to make sure the algae does not return.

“There’s a chance it could come back, so we’re going to keep an eye on this,” Jones said. “We err on the side of caution. We will close the lakes again if the toxic algae turns up. We keep an extremely close eye on the lakes that people go swimming in.”

Toxic algae can be highly visible, or not visible at all. In the photo above, algae can be seen at Lake Anza in September. Photo: Sunshine Townsend/EBRPD

Humans can experience skin irritation and gastrointestinal symptoms when exposed to the algae, which has been a significant problem due to the ongoing California drought.

Warmer-than-usual water related to the drought caused outbreaks in numerous places in California last year, including the Russian River, Jones told Berkeleyside previously.

Lake Del Valle and Lake Chabot still contain the algae, and have not reopened.

In other park news, EBRPD staff have asked the public to stay off several Tilden Regional Park trails during wet weather, due to mud and erosion, including Vollmer, Wildcat Gorge and Arroyo trails.

If hikers find trails blocked by fallen trees or otherwise damaged, they should let park staff know so they can fix the problem, Jones said.

Read more about toxic blue-green algae on the park district’s website. Get the latest information on Lake Anza.

How the California-wide drought is affecting Berkeley (10.20.15)
Lake Anza closed to swimming due to toxic algae (09.17.15)

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Emilie Raguso (former senior editor, news) joined Berkeleyside in 2012 and covered politics, public safety and development until her departure in 2022. In 2017, Emilie was named Journalist...