Latest algae bloom, in Discovery Bay, threatens way of life

Water in a lagoon is lime green in color near Newport Drive and Capstan Place in Discovery Bay, Calif. on Tuesday, July 26, 2016. Contra Costa County officials may issues warnings if toxic levels of algae is detected from samples collected from the water. less Water in a lagoon is lime green in color near Newport Drive and Capstan Place in Discovery Bay, Calif. on Tuesday, July 26, 2016. Contra Costa County officials may issues warnings if toxic levels of algae is ... more Photo: Paul Chinn, The Chronicle Buy photo Photo: Paul Chinn, The Chronicle Image 1 of / 18 Caption Close Latest algae bloom, in Discovery Bay, threatens way of life 1 / 18 Back to Gallery

Shannon Sandbank and her family moved to Discovery Bay last year for the same reason everybody does: to soak up life on the water.

The community east of Brentwood was created in the 1960s on man-made islands that finger through a bay that was once delta farmland, with many homes featuring boat docks in their resort-like backyards.

But dreams of Jet Skis and human cannonballs have been put on hold by a nasty bout of algae that has dramatically worsened in recent weeks — an unwelcome and possibly harmful intrusion that scientists say marks the latest in a string of troubling algal blooms in California and across the nation.

Video: Discovery Bay Residents Warned To Stay Out Of The Water

“All of a sudden the water starts getting greener and greener and I thought, ‘I don’t know if I’m going to let my kids go in that,’” Sandbank, who lives with her husband and four of their children in an attractive waterfront subdivision, said on Tuesday. “Now we just go to the community pool.”

Colorful blobs of algae in some Bay Area lakes have prompted health warnings, leading many people to rethink wading in or to put their dogs on a leash, lest they jump in to cool off. But the plumes off the Sacramento-San Joaquin River Delta are threatening a whole lifestyle.

“We used to go out in our boat every night when my husband got home, but not anymore,” Sandbank said.

Defeated, they recently moved their boat 90 miles away to Don Pedro Reservoir in Tuolumne County.

Health warning

This week, Contra Costa County’s health department weighed in, warning residents in the town of about 13,000 to avoid contact with the water — that includes dogs — after preliminary tests revealed the presence of cyanobacteria, or blue-green algae.

The microscopic organism, named after the Gatorade-colored sheen it creates, produces a toxin that can cause rashes, eye irritation and gastrointestinal upset. It’s rarely fatal for humans, though dogs often die when they drink too much infested water.

Similar plumes of blue-green algae have prompted health advisories in recreational lakes and reservoirs across California, from Clear Lake to ponds in the East Bay hills to Southern California’s Pyramid Lake.

Elsewhere, the algae has closed beaches and businesses along Florida’s touristy east coast, sickened swimmers and fishermen in Utah Lake, and put Lake Erie under close observation due to contamination of drinking water supplies.

While the blooms are naturally occurring, scientists say their preferred conditions have abounded lately: warm sunshine and plenty of nutrients, often pollutants.

“The frequency and duration of these algal blooms seems to be increasing,” said William Cochlan, a senior research scientist at San Francisco State University, while noting a trend that’s occurred for at least a decade. “Some of these are just natural events, and some may be exacerbated by human activities.”

Fertilizers and septic runoff, which the algae thrive on, have been a big driver of mucky masses in many parts of the country, experts say, while in California the drought has shrunken rivers and lakes, allowing sunlight to more easily penetrate the water.

A giant algal bloom off the coast of California last year, though a different organism than the one tainting freshwater supplies, was a product of record-breaking ocean temperatures that were, in part, blamed on climate change.

The proliferation of pseudo-nitzschia, which produced the neurotoxin domoic acid, prompted the closure of the state’s crab season for several months, because the crustaceans weren’t safe to eat.

‘I’m still swimming’

In Discovery Bay, the greenish waters have some residents more alarmed than others.

“I’m still swimming,” said Bob Harper, 71, who bought a waterfront home this year after selling his house in San Francisco. “In the afternoon, we’ll jump in the bay to cool off. We use it as a pool.”

His dog, Cabo, didn’t mind playing in the water, either.

“She’s not a swimmer, but she likes to get wet,” Harper said.

While county health officials confirmed the presence of blue-green algae this week, they are awaiting the results of more comprehensive tests to determine the scope of the problem.

“It could be a very big concern, but we have to get the numbers back from the lab,” said Marilyn Underwood, director of the county’s Environmental Health Division. “In the interim, we’re being cautious and saying, ‘Just stay out of the water and keep your pets out of the water.’”

Kurtis Alexander is a San Francisco Chronicle staff writer. Email: kalexander@sfchronicle.com Twitter: @kurtisalexander