Algae in Bay Area lakes: Is it safe to swim?
Aubree and Mila, 7 and 3, Lepley splash in East Bay Regional’s Lake Temescal in Oakland on Thursday. Lake Temescal is open for swimming this year, while it was closed for long periods last year due to a bloom of toxic blue-green algae. (Laura A. Oda/Bay Area News Group)
OAKLAND — Before taking their children to an iconic East Bay swim lake, a group of parents last week called ahead to make sure the Lake Temescal water wasn’t toxic.
It was safe and the reservoir was open, unlike long stretches last year when blue-green algae called cyanobacteria caused swimming to be banned at Lake Temescal and 22 other California lakes or waterways.
“We definitely checked before coming,” Erin King, an Oakland mother, said as she relaxed on the sandy beach at the lake in hills near the Caldecott Tunnel. “When we’re told the water is okay, I’m not concerned. But we are paying attention.”
As warmer weather kicks off the outdoor swim season, California water officials say that lake operators are more vigorous about posting advisories and the public is more informed about the risks than two years in the drought when a surge in problems left officials scrambling to cope.
“There is more awareness of cyanobacteria,” said Ali Dunn, an environmental scientist with the state Water Resources Control Board. “People should be aware of their surroundings and its risks, whether it’s poison oak or things in the water.”
The state has a website on harmful algae blooms.
It’s too early, Dunn said, to say whether 2017 is going to produce more blue-green algae problems than last year.
While the algae has been detected in 49 California lakes or waterways so far this year, the blooms have turned toxic in only three of them requiring swim areas to close, the state water board reported Friday.
The naturally occurring algae can be detected in lakes without causing health problems for long periods, but the algae also can transform within a few days into something toxic that can kill dogs that drink it and cause gastrointestinal problems in humans that consume it.
East Bay Regional Park District officials say the algae has been detected this year at five swim lakes but only one of them, the swim area at Quarry Lakes Regional Park, is closed for health reasons. Quarry Lakes, former quarry pits mostly filled by groundwater, has limited water circulation.
Lake Temescal in Oakland, Del Valle Reservoir in Livermore, Lake Anza in Tilden Park in Berkeley, and Shadow Cliffs Recreation Area in Pleasanton, remain open as tests show the blue-green algae in the water is not producing toxins.
“We test the water regularly, and post the results on our website,” said Hal Maclean, the regional park district’s water quality manager. “We want people to take a look at the testing results.”
Dunn credited the regional park district with an aggressive warning policy.
Those reservoirs have two kinds of advisory signs. One says the water is safe for swimming.
The other, marked yellow, says blue-green algae is present, but it has not made the water unsafe. Visitors are urged not to swallow the water, to shower or bathe after swimming in the water, and not to let dogs consume the water.
Dogs are particularly vulnerable to cyanobacteria attacks on the liver. Some have died within 30 hours after lapping up water, or licking the moisture off their fur, state health officials said.
Cyanobacteria, which live in water and manufacture their own food, are microscopic, but they can multiply and bloom into colonies that are visible. The bacteria have been around for about 3.5 billion years, according to a University of Berkeley fact sheet.
Thriving in stagnant water, blue-green algae blooms increased during California’s drought from 2012 to 2016.
While heavy storms ended the drought last winter, the big runoff also washed into lakes heavy loads of nutrients, another contributor to blue-green algae, officials said.
Brenda Calderon, a San Leandro mom, said she was disappointed last year when Lake Temescal was closed much of the swim season, and she couldn’t take her son and daughter to swim and wade there.
“I like this place because the children can get outside, get fresh air, see trees,” Calderon said during a lake visit last week. “I really miss the lake when it’s closed.”