Sergio Flores, 39, disappeared in the water at Winton Park in Fresno County around two o'clock Sunday afternoon.
A helicopter later spotted his body about three miles downstream from the picnic area where he entered the river.
Fresno County sheriff's deputies say Flores went into the water to help his son. The boy was able to make it to the shore, but the current pulled his father under.
The fast-moving water also made it difficult for the sheriff's boating unit to reach Flores, but deputies were eventually able to recover his body.
Sgt. Brent Stalker said, "Deputies say this is the second confirmed drowning on a Central Valley river this spring.