A triathlete died early Sunday morning during the swimming phase of the Escape from Alcatraz Triathlon.
A source who wished to remain anonymous said the victim is 46-year-old Ross Ehlinger of Austin, Texas.
It is believed he suffered a massive heart attack shortly after jumping into the 51-degree waters just off Alcatraz Island at 7:30 a.m.
The water safety team saw him in trouble seconds after he dove off the California Hornblower. They immediately pulled him out and performed CPR as he was transported to land, but were unable to revive him.
Though the triathlon was held three months earlier in cooler weather to make room for the America's Cup in June, race director Bill Burke told the San Francisco Chronicle that the cold temperature did not contribute to Mr. Ehlinger's death.
"Was it colder than normal? Yes. But in my opinion, the water temperature was not a factor at all in this tragedy," Burke said. "The gentleman obviously had a heart condition he was unaware of."
Organizers said this was the first death in the 33-year history of the event.
"The thoughts and prayers of the entire Escape from Alcatraz Triathlon team are with the family and friends of the racer as they mourn this loss," said Burke.
Nearly 150 swimmers had to be rescued Sunday, more than three times the normal number.
The Escape from Alcatraz Triathlon attracts annually more than 2,000 professional and amateur competitors from around the world. The race includes a 1.5-mile swim from Alcatraz Island to the shores of San Francisco, an 18-mile bike ride and an 8-mile run through the Golden Gate National Recreation Area.