Signs cautioning visitors about the potential dangers of harmful algae in the Russian River will remain posted at Sonoma County beaches after very low levels of a naturally produced neurotoxin were detected in the water again this week, county health officials said.
Weekly sampling at 10 popular beaches turned up Anatoxin-a at two of them: Steelhead Beach in Forestville and Johnson’s Beach in Guerneville, the county’s environmental health division said.
Last week, the water in front of three other beaches tested positive: Patterson Point, downstream from Monte Rio; Del Rio Woods Beach in Healdsburg; and Cloverdale River Park Beach. Samples collected at those beaches this Monday were free of the substance, according to lab results posted online Thursday.
In every case, the measurable level of neurotoxin was extremely minimal, at least 80 times below the threshold that would oblige health officials to close a beach to swimming and other water recreation.
But with Anatoxin-a, the state requires posted warnings at any level of detection because of the risks associated with ingestion. In large amounts, Anatoxin-a can prove fatal to humans, livestock and pets, as it did with two dogs who died in the summer of 2015 after frolicking in the Russian River near Healdsburg.
Though river beaches remain open, visitors are urged to take precautions to reduce the threat of accidental ingestion, especially by children and pets.
“We just want people to be careful,” Deputy Sonoma County Health Officer Karen Holbrook said Thursday.
Blue-green algae, formally called cyanobacteria, are not actually algae at all. They are primitive, photosynthesizing organisms related to bacteria that bloom prolifically in warm, slow-moving water well-fed with nitrogen and phosphorous.
Though not all are dangerous, some produce toxins that are released when the cells rupture, and can cause severe illness.
Outbreaks of harmful algae have become increasingly common in freshwater lakes, streams and ponds around the globe in recent years, including Northern California and the North Bay region, though often involving different types of harmful algae. Anatoxin-a has been detected in the Russian River in each of the past two years, as well, and prompted alarm in the weeks before Labor Day 2015, when a beloved retriever visiting with his family from the South Bay suddenly became violently ill and died.
The substance attacks the nervous system and can cause muscle cramps, lethargy, confusion, memory impairment, convulsions, respiratory paralysis or cardiac failure.
Studies indicate dogs are actually drawn to blue-green algae because of its odor and are prone to eating it, causing them to ingest large quantities of the toxin. Sonoma County Regional Parks operates five public beaches on the Russian River.
Park Programs Manager Dave Robinson said there has been an observable reduction in visitors since the county first posted signs about potential toxins July 26, including some who have turned around after seeing the notices and gone elsewhere.
But many people continue to enjoy the river, swimming and boating as usual, including “hordes” of corporate buses from the Bay Area loaded with people out to have fun.
“The signage on the blue-green algae hasn’t stopped them at all,” he said.
The county’s day camp operations continue as usual, as well, including a recently completed day camp session in which campers kayaked and paddleboarded down the river, practiced self-rescue and other skills.