A 46-year-old man died at Alcatraz Triathlon of a heart attack while swimming in the Escape from notorious prison in Northern California Sunday morning.

"We have reason to believe the gentleman suffered from a massive cardiac event as he entered the water and began the swim," race officials said in a statement.

The man from Austin, Texas whose name was not released died less than a minute after jumping into the San Francisco Bay, which was about 10 degrees cooler than last year's water temperature as the race, was held three months earlier.

"Was it colder than normal? Yes. But in my opinion, the water temperature was not a factor at all in this tragedy," Bill Burke, the race's director, told the San Francisco Chronicle. "The gentleman obviously had a heart condition he was unaware of."

The death is the first in the 33-year history of the event, according to organizers. The triathlon's water safety team noticed the man and began performing CPR as they rushed him to shore, but rescuers were not able to revive him.

The triathlon is among the most challenging in the world that starts with 1.5 mile swim from Alcatraz Island followed by an 18-mile bike ride and an 8-mile run through San Francisco along the waterfront and through Golden Gate Park.

"What happened today was very, very sad," Burke said. "It underscores that athletes need to be checked carefully by a cardiologist before pushing themselves."