The man was swimming on the north side of the lake in Madera County.
Authorities do not know when he went under, but at about 7 pm he was pulled to shore by Good Samaritans, who called for help.
CAL FIRE crews and state park rangers rushed to the scene, and the man was airlifted to a hospital.
Authorities say he was not wearing a life jacket and was swimming in a part of the lake where there are no lifeguards.
Stay with Action News for updates on this developing story.