Lake Anza South Swim Beach photographed on Aug. 29, 2016. Photo: Hal MacLean
Lake Anza South Swim Beach photographed Aug. 29. Photo: Hal MacLean

The East Bay Regional Park District has closed Lake Anza to swimming due to high levels of toxic algae. The decision was made after tests showed the toxin Microcystin had reached dangerous levels, and the news came before the official swim season ends next Friday, Sept. 9.

It’s the second consecutive year EBRPD has been forced to close Lake Anza. It did so last September, along with several other lakes in the district, including Quarry Lakes in Fremont, Lake Temescal in Oakland. Heavy El Niño rains cleared the toxic blue-green algae from Lake Anza by late January.

EBRPD spokeswoman Carolyn Jones said, “Hydrologists test the water for toxicity a couple of times a week and once it gets over a certain threshold we have to close the lake. If the levels are just low we issue a warning.”

On Monday tests showed there were 15 parts of Microcystin per billion near the lake bridge.

Jones added: “We are not happy about having to do this. It’s a beautiful and popular lake and we hate to close it. We thank the public for their patience.” Jones said other lakes in the district were still open for swimming, including Lake Temescal and Quarry Lakes.

Blue-green algae can be fatal for dogs, and Jones stressed that dog owners should not allow their pets into Lake Anza. Three dogs died in 2015 after drinking from Lake Chabot, where the algae had cropped up.

Humans can experience skin irritation and gastrointestinal symptoms when exposed to the algae.

The reason for the toxicity of the algae is something of a mystery although it is related to climate change, Jones said. “It’s one of the great mysteries of science,” she said. “We know algae is associated with warm or stagnant water, but why it becomes toxic is not completely understood. It’s being studied by scientists and is a global phenomenon, also seen in places like the Great Lakes and China.”

EBRD put up signs warning people not to swim in Lake Anza. They stress that people should have “no bodily contact” with the water in the lake; pets, especially dogs must be kept out of the water; skin that does come into contact with the water should be “rinsed with tap water;” and that fish from the lake may be consumed only after removing guts and liver and rinsing fillets in tap water.

Jones said the district would not be treating Lake Anza with chemicals to eradicate the toxins, as it has done in the past with Lake Temescal. That decision was made because Temescal is a small lake and the bloom happened early in the swimming season. But the process is expensive, Jones said, and “nobody likes putting chemicals in a lake.”

Instead, she said, the district will hope the problem goes away and let nature take its course.

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

After rains, some East Bay lakes now free of toxic algae (02.01.16)
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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Tracey Taylor is co-founder of Berkeleyside and co-founder and editorial director of Cityside, the nonprofit parent to Berkeleyside and The Oaklandside. Before launching Berkeleyside, Tracey wrote for...