Increase in rainfall flushes out toxic algae in Tilden Regional Park’s Lake Anza

Ashish Samaddar/File

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A recent increase in rainfall in the East Bay has flushed out toxic algae from Tilden Regional Park’s Lake Anza.

Lake Anza closed in September 2015 when East Bay Regional Park District officials discovered unsafe levels of microcystin, a toxin produced by blue-green algae, which thrives in warm climates. Two months earlier, EBRPD officials shut down Oakland’s Lake Temescal because of a similar occurrence of algae-related lake toxicity.

Both lakes were closed for most of the 2015 swim season, according a December EBRPD board meeting agenda. Since EBRPD discovered the algae in September, funds have been allocated to the district’s Water Resources Management Unit to monitor lake toxicity on a weekly basis.

According to EBRPD spokesperson Carolyn Jones, Lake Anza has not had any toxicity readings for more than two months, when the rains first began.

“We will continue to do the testing religiously,” Jones said.

Jones added that the dissipation of lake toxins has been completely naturalEBRPD has tried to take steps to reduce the possibility of algae growing, but Jones said using chemicals is the district’s last resort.

The lake is expected to reopen in April in time for swim season, Jones said, though algae may return if temperatures rise again. According to Jones, a similar phenomenon occurred in Lake Temescal, which has produced toxic algae on and off for a couple of years.

“People’s dogs swim in Lake Anza,” Jones said. “People swim in the lake. We have to be extremely cautious.”

No one, including the district’s staff, is completely sure what causes the algae to become toxic, according to Jones.

The first-ever toxic algae bloom in the East Bay occurred in 2014, EBRPD officials reported last year. They emphasized the impact of California’s drought on the incident, citing in particular the lake’s unusually low water levels and warmer temperature.

EBRPD will continue to warn people of the algae’s presence in the lakes with signs and online notices, but Jones said the district hopes the outbreak will not resurface.

“We appreciate everyone’s patience,” Jones said. “(Lake Anza is) a beautiful lake, and it would be a drag to see it closed down in the middle of summer.”

Contact Harini Shyamsundar at [email protected] and follow her on Twitter at @hshyamsundar.