People are being asked to stay away from the lower Russian River after an unknown volume of untreated wastewater spilled from a sewage treatment plant in Guerneville during the tail-end of a storm that drenched Sonoma County and flooded many roads across the region.
Heavy overnight rainfall — part of the region’s prolonged atmospheric river — caused storage ponds at the facility to overflow early Tuesday morning, said Stuart Tiffen, a spokesman for Sonoma Water, which operates the Russian River Treatment Plant.
Affected residents were alerted of the spill Tuesday morning, officials said.
Tiffen described the spill as an “ongoing situation” and said it is currently unknown how many residents are impacted or how much wastewater, including raw sewage, is spilling into the river.
“It is difficult to really gauge right now,” Tiffen told The Press Democrat.
Multiple agencies are working with Sonoma Water to address the spill, including the Sonoma County Sheriff’s Office and the county’s environmental and public health offices.
Officials did not provide a timeline for the cleanup, warned people to avoid contact with the water and asked users to reduce wastewater use.
Amid the heavy rain fall, the plant received flows at a rate of four million gallons per day and the facility had no additional storage capacity, since it is designed to hold 710,000 gallons a day during dry conditions, officials said.
The Russian River, swollen and murky from recent rains, was flowing at a very high rate Tuesday, exceeding 30,000 cubic feet per second, or 13.4 million gallons per minute, as measured at the Hacienda Bridge in Forestville.
Some of the discharge was traveling a quarter of a mile through a forested area before it reached the mainstem of the river, officials said.
Sonoma Water notified the regulatory agencies and environmental specialists, who they say will assess the conditions and potential environmental impacts.
Tuesday was not the first time Sonoma Water reported a wastewater spill.
In March 2024, more than 200,000 gallons of partially treated water spilled into the river following a power outage at the treatment facility.
Three years earlier, a sewer main break sent sewage gushing out of a pipe in the Vacation Beach area of Guerneville. The system also experienced a pipeline break in 2014.
Contact Staff Writer Anna Armstrong at anna.armstrong@pressdemocrat.com. On X (Twitter) @annavarmstrongg.