An adult mosquito sample found in southeast Petaluma tested positive for West Nile virus, according to the Marin/Sonoma Mosquito and Vector Control District.
It was the second sample to test positive this year in the two counties.
The mosquito sample was taken from the vicinity of the Ellis Creek Water Recycling Facility. As a result, the district said it initiated larval mosquito control actions today and will increase surveillance efforts.
Informational signs will be posted along walking trails at the water recycling facility, the district said.
Residents were reminded to cover septic tanks, secure screens to windows and vent pipes, and wear long clothing and insect repellent while outdoors.