Napa County Sheriff's Lt. Tracey Stuart said 26-year-old Tyron Terrell Jenkins was swimming at Acorn Beach in the Oak Shores Day Use Area at about 3 p.m.
Two of his female friends noticed him struggling and panicking in the water about 15-20 yards from shore, Stuart said. However, they were unable to pull Jenkins from the water, Stuart said.
The sheriff's department dive team responded and found Jenkin's body at about 5 p.m. in 22 feet of water, Stuart said. An autopsy is scheduled for Thursday.
Jenkins' friends had been drinking alcohol but Jenkins was not, Stuart said.
It was the fifth drowning at the lake since Jan. 1, Stuart said.
On Monday afternoon, Jonatan Roberto Najera-De La Fuente, 23, of Richmond drowned near Foxtail Flat in the Oak Shores Day Use Area.