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Sonoma County health officials say the risk of toxic blue-green algae in the Russian River has subsided enough that they will suspend weekly testing of water and algae samples taken from 10 popular beaches between Cloverdale and the outskirts of Monte Rio.

Still, health warnings posted at local beaches will remain in place until temperatures drop sufficiently and — with luck — rain arrives to increase river flows, eliminating some of the conditions that nurture algae.

Also, dogs should still avoid the water “out of an abundance of caution,” said Deputy Sonoma County Health Officer Karen Holbrook, and visitors should continue to adhere to a list of “healthy water habits” aimed at preventing adults and, especially, young children from inadvertently ingesting algae or river water containing dangerous toxins.

The update came Friday in what has become a weekly bulletin issued by the county Department of Health Services in the wake of the Aug. 29 death of a golden retriever that consumed river water while on a canoe trip with its owners, a San Jose couple.

While the span and constant motion of the Russian River make it impossible to say the entire watershed is completely clear of isolated, potentially dangerous algae specimens, the neurotoxin responsible for the dog’s death was not detected during the past two weeks of testing at the county’s 10 most frequented beaches, health officials said.

Testing previous to that had revealed only “very low levels or undetectable levels” — nothing that would trigger a need to close the river to humans, according to Deputy County Health Officer Karen Holbrook.

Holbrook said county health and North Coast Regional Water Quality Control Board personnel would continue to monitor the river for new blooms and overall conditions that might add to concerns.

“As the river is a constantly changing environment and the conditions are still present which could allow algae to grow, we are keeping the signs up and encouraging healthy water habits,” Holbrook said.

The Russian River is one of numerous water bodies in California subject to public warnings because of the presence of certain bacteria — commonly known as blue-green algae — that can produce potentially lethal toxins.

The cyanobacteria thrive in warm, still, shallow water — the conditions made more prevalent by summer’s heat and the extended drought affecting the state. Higher levels of nutrients that are often linked to human activity, including nitrogen and phosphorous, can help fuel the bacteria’s growth.

Cyanobacteria “is something that sits around, essentially dormant, and just waits for the right conditions to kind of spring to life,” she said.

It can replicate very quickly, creating a kind of “pea soup” appearance in stagnant water, Holbrook said.

Problem areas have included the Eel River in eastern Mendocino County, where a dog perished after swimming near a Potter Valley campground early last month. Testing determined that dog succumbed to a powerful neurotoxin called Anatoxin-a — the same substance that killed Posie, the San Jose couple’s dog, which suffered an awful death after paddling around and splashing in the Russian River downstream of Healdsburg.

The latest alarm has been sounded in Sacramento, where the death of a dog that swam in the Sacramento River at a city park prompted health officials Thursday to advise the public to avoid any river, lake, pond or other body of water with visible scum layers, large mats or other visible blue-green algae blooms.

Last week, Santa Cruz County environmental health officials issued a warning about a blue-green algae bloom in the lower San Lorenzo River. Blue-green algae blooms also closed Lake Anza in Berkeley’s Tilden Park to swimming last month.

Quarry Lakes in Fremont and Lake Temescal in Oakland were closed earlier in the summer.

In Sonoma County, health officials first made the public aware of blue-green algae in the Russian River on Aug. 20, saying the substance was found growing amid mats of harmless filamentous algae in slow, shallow side pools on the river.

It was closer to Labor Day, in the wake of Posie’s death, when concerns rose sufficiently that health officials contemplated closing the river to human recreation.

But the toxin levels never reached a threshold that would have triggered a closure, with the risk of contact minimized as long as people refrained from drinking or cooking with the river water, Holbrook said. Dogs, on the other hand, tend to drink the water they swim in and then lick their bodies afterward, putting them at high risk of consuming potentially toxic algae, she said.

Testing of the Russian River has continued for seven weeks at Cloverdale River Park; Del Rio Woods Beach, Camp Rose Beach and Healdsburg Veterans Beach in Healdsburg; Steelhead Beach, Forestville Access (or Mom’s) Beach and Sunset Beach in Forestville; Johnson’s Beach in Guerneville; Monte Rio Beach; and Patterson Point in Villa Grande.

Don McEnhill, executive director of the nonprofit group Russian Riverkeeper, is among those who say rising average temperatures are likely to take their toll on water resources and promote more frequent blue-green algae blooms of the sort that began gaining notice in the early 2000s.

“This is a symptom of the fact that climate change in California is a water problem,” McEnhill said, “and this is one of the symptoms that we’re going to be looking at — probably, unfortunately — more frequently around the state because these conditions are going to be more prevalent, more often.”

The federal Centers for Disease Control National Outbreak Reporting System logged only three freshwater disease outbreaks associated with harmful algae blooms between 1978 and 2008. In 2009 and 2010, there were 11, according to a study released early last year.

The rising incidence is behind plans underway for a regionwide workshop next spring to bring together health and water agencies to spread awareness of the evolving science around blue-green algae and to develop consistency plans for testing and public health action, said Clayton Creager, environmental program manager with the North Coast Regional Water Quality Control Board.

There will be time for the public to participate, as water users will need to be more involved in monitoring and more adept in identifying blue-green algae.

“It doesn’t matter whether you believe humans are the primary driver of climate change or not,” McEnhill said. “It’s happening, and there are consequences, and this is one of them. It wouldn’t be very smart to close our eyes to this possibility and not be prepared to address it.”

You can reach Staff Writer Mary Callahan at 521-5249 or mary.callahan@pressdemocrat.com. On Twitter @MaryCallahanB.

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