Pacific Gas and Electric says the Lake Spaulding reservoir in Nevada County could fill and the dam could begin spilling as soon as Saturday.
If that happens, flows on the South Yuba River would be above the normal season flows for this time of year.
PG&E recommends anyone planning to be near rivers and streams to be aware of the higher flows and take precautions.
The dam could spill for several days, depending on rains.
Flows would be higher along about 40 miles of the South Yuba River between Lake Spaulding in Nevada County and Englebright Lake in Yuba County.
The river is able to handle much higher flows like those that occur during the wettest months of winter.