The Petaluma River reached flood stages Sunday morning, and forecasters warned heavy rainfall was expected to continue throughout the day.
The National Weather Service's flash flood warning was in effect until 12:45 p.m. for the Petaluma area.
"The river is coming up in a hurry," meteorologist Diane Henderson said.
Stream gages at Willow Brook at Penngrove Park, Willow Brook at the Old Redwood Highway Bridge and Willow Brook at Stony Point Road were at or above flood levels.
Rainfall caused problems throughout the county.