The Los Angeles Times reported Sunday that the boy was swept away at a popular boating and swimming destination called Three Mile Slough.
The delta area of the Sacramento and San Joaquin rivers is about 40 miles (64 kilometers) south of Sacramento.
The boy was pulled from the water and wasn’t hurt but three of his relatives were pulled under after they went in after him, said Rio Vista Battalion Chief Brandon Wilson.
People “saw them go under and never saw them come back,” Wilson said.
Authorities searched for the men for two hours in hopes of rescuing them but later transitioned to a recovery operation, the San Francisco Chronicle reported.