Wilson Lauvao of San Diego, 51, was pronounced dead at UC San Diego Medical Center on Saturday afternoon, less than an hour after he was pulled from the water.
Lifeguards saw him being pulled to shore at about 12:30 p.m. off Mission Bay Drive and Bayside Lane, and immediately responded.
Lifeguards performed CPR until paramedics arrived. The paramedics then took over advanced cardiac life support and Lauvao was taken to the hospital, according to a statement by the medical examiner.
Emergency room personnel continued attempts to revive Lauvao, but despite aggressive resuscitative efforts, he could not be revived and his death was pronounced shortly after arrival at the hospital at 1:22 p.m.
Lauvao had been floating face down in the water, about 15 feet from shore for an unknown period of time when he was discovered unconscious by others in the water, Lt. Rick Romero of San Diego Lifeguard Service said.
The medical examiner's office was investigating Lauvao's cause of death.