Sonoma County officials posted caution signs at beaches up and down the Russian River on Wednesday alerting visitors to positive test results for a potentially dangerous, naturally occurring neurotoxin linked to harmful algae, a problem surfacing around Northern California this summer.
Water samples collected at three local beaches turned up very low levels of a substance called Anatoxin-a, which is produced by certain species of blue-green algae, Sonoma County health officials said.
It’s the third year in a row the algae-related toxin has been detected in the river.
The most-recent samples were taken Monday and the test results received Wednesday, Sonoma County Health Officer Karen Milman said.
Though the level of toxin in the water “was just at the ability to detect it,” the finding triggers precautionary alerts under state guidelines, she said.
Rivergoers should be particularly watchful of dogs, which are actually attracted to harmful algae, according to studies, and, by virtue of their relative body size and habits when around fresh water, are particularly susceptible to exposure.
But swimmers, waders, tubers, paddle boarders and others who may have direct contact with water, as well as parents of small children, should take precautions to ensure they do not put themselves or their offspring at risk, health officials said.
That means avoiding ingesting river water or cooking with it, washing off after swimming and avoiding hand-to-mouth contact.
“Be aware and take precautions to protect themselves, particularly their pets, but also know that the river is open,” Milman said.
The news, if not entirely surprising, is disappointing for business owners dependent on the river, coming at high season for tourism.
After three consecutive years, and with the toxin levels so low, many said they thought most visitors would continue to enjoy local beaches and boating, though some unknown number will stay away, they said.
“I think the newness of these warnings has warn off, so people realize that the risk is low,” said Dan Poirier, co-owner of Johnson’s Beach & Resort in Guerneville.
John Menth, a county parks lifeguard who also runs his own paddle boarding rental and tour company, said he was at Healdsburg’s Veterans Memorial Beach on Wednesday when county personnel came to post the caution signs.
Some arriving visitors “turned right around and left,” he said, forecasting some impact on river business.
But he and others said they hoped people would understand they are not at risk “if they don’t go down there and drink the water.”
The Russian River notification comes in the wake of a broader alert from the North Coast water quality regulators about the potential for harmful algal blooms in fresh water bodies around the region — including Lake, Mendocino and Humboldt counties — as a result of summer conditions that include warming water temperatures and slow-moving water.
Algae-related toxins already have been reported at several sites around Northern California this year, including in Clear Lake and in Upper and Lower Blue Lakes, all in Lake County.
Blue-green algae is reportedly widespread in Clear Lake, though samples that tested positive for toxins in early July were at very low levels, mostly from the most southerly parts of the lake, according to Sue McConnell, a program manager with the Central Valley Regional Water Quality Control Board, with jurisdiction over most of Lake County.
A dense bloom in the lake’s upper arm also is believed to have contributed to a fish kill that left hundreds, perhaps thousands of fish dead this week near Clearlake Oaks, apparently after they suffocated in water that had been depleted of oxygen, Lake County Water Resources Director Phil Moy said.
In that case, the fish are not believed to have died as a result of toxin, but because the blue-green algae, formally known as cyanobacteria, use oxygen at night and give off carbon dioxide, creating low oxygen levels, he said.
Toxic concentrations of two harmful algae also were detected in a Napa River pond where two dogs died last month, while a toxic bloom was reported last week in Lake County’s Copsey Creek.
The South Fork of the Eel River, which crosses into northern Mendocino County from Humboldt County, also is historically a common hot spot for toxic algae blooms.
Sonoma County health officials and state quality water regulators have been monitoring conditions in the Russian River closely since an outbreak of harmful algae the summer of 2015 led to the deaths of two dogs.
In both cases, Anatoxin-a appeared to be responsible, causing violent, sudden illness and death within moments of exposure.
Caution signs were posted again last year on the Russian River after routine testing revealed low levels of the substance. This year, seasonal testing began July 17 after river monitoring suggested the kinds of conditions in which blue-green algae, or cyanobacteria, thrive, Milman said.
All 10 beaches that are part of the testing protocol were clear last week.
Test results received Wednesday showed that samples from Cloverdale River Park Beach, Del Rio Woods Beach in Healdsburg and Patterson Point beach, downstream of Monte Rio in the community of Villa Grande, all had barely detectable levels of Anatoxin-a, measured between 0.14 and 0.16 micrograms per liter.
Under state guidelines, any detection of neurotoxin triggers cautionary notification about a water body.
Danger warnings that prohibit swimming and other activities in the water are not required until the toxin level reaches 20 micrograms per liter, or about 130 times what was detected early this week.
The bilingual caution signs posted Wednesday say that harmful algae “may be present” in the water and urge the public to avoid algae and scum while swimming, to keep children away from the shoreline, to prevent animals from drinking the water or eating scum, to avoid drinking or cooking with the water, to throw away the guts and clean fillet of any fish caught in the river and to avoid eating shellfish caught in the river. Larry Laba, owner of Healdsburg-based SOAR Inflatables and Russian River Adventures, lost his own dog during the 2015 bloom and said he was contacting customers who had reserved space for dogs on their boating tours to inform them of recent developments and offer refunds.
He noted that the toxin level in the river when his dog died was several hundreds times what it is right now.
“I’m not encouraging them to come (with dogs),” he said. “I’m encouraging them to make a smart choice, is the best way I can put it.”
Water quality experts say harmful algal blooms have become more common and persistent in recent years, possibly related to changing conditions linked to global warming.
Blue-green algae tends to thrive in warm, slow-moving, shallow water, which is why it tends to peak in the latter part of summer and was prominent during California’s recent drought.
Officials also are wary of the impact this year of voluminous runoff that likely loaded streams and lakes with phosphates and other nutrients on which blue-green algae could feed.
Heightened awareness, closer monitoring and more refined testing may be alerting the public to blooms they wouldn’t have known about even a decade ago, officials said.
“That’s a big part of the dynamic,” said Don McEnhill, executive director of the Russian Riverkeeper. “We never looked before, and there could have been these very low concentrations that we weren’t aware of before.”
You can reach Staff Writer Mary Callahan at 707-521-5249 or firstname.lastname@example.org. On Twitter @MaryCallahanB.