Doctors may never know precisely what killed open water swimmer Fran Crippen, the 26-year-old who died during a race in Abu Dhabi over the weekend, but they agree that strenuous exercise in hot water could result in fatal heat stroke.
Had a safety boat been near the elite swimmer when he lost consciousness, he might have been cooled down and been saved, they say.
"It's pretty straightforward -- he died of one of two things," said Dr. Mark Morocco, associate professor of emergency medicine at the UCLA School of Medicine.
"He drowned of a cardiac arrhythmia or he died of drowning because he passed out," said Morocco, who has never treated Crippen. "Both were directly related to over-exertion, which is a terrible garbage-can diagnosis and does not speak to what happened."
"In the age of kayaks, jet skis and outboard motors, this sort of thing should never happen to an elite swimmer," he said. "No one was there to help him up out of the water."
USA Swimming said Monday it would commission a full, independent investigation into Crippen's death.
Some earlier reports indicated that the Olympic-bound athlete died of a heart attack. The findings of an autopsy by local authorities have not been released. And even that may not give definitive answers.
Heat stroke, for example, could only be determined if doctors got an internal body temperature right after Crippen died. His body wasn't found until two hours after the race ended -- about 400 meters from the finish line.
The International Swimming Federation (FINA) said doctors ruled the cause of death as severe fatigue.
Crippen's sister Maddy, herself an Olympic swimmer, told "Good Morning America" that her brother had been voicing concerns for months about inadequate safety.
A native of Philadelphia, Crippen was "fit as a fiddle," according to his former high school coach from Germantown Academy, Richard Shoulberg.
Crippen had told Shoulberg just 12 hours before the race that the outside temperature was 100 degrees and that the water was 87 degrees. Several swimmers complained of dehydration and disorientation and three were taken to the hospital.
"l have heard lot people complaining about the water being too warm," said Bill Volckening, a former editor of Swimmer magazine for U.S. Masters swimming. "There are some dangers of hyperthermia that have not really come to light yet and I hope there is some major reform in the sport of open water swimming with regard to safety."
Volckening, who knew Shoulberg as a high school swimmer, said the coach's athletes were "extremely smart, extremely savvy and extra well prepared."
"I don't have a good opinion of FINA -- they mismanage anything that comes their way," he said.
Those who trained with Crippen said he also used GU energy gel a replenishing liquid that contains high amounts of caffeine. The swimmer reportedly consumed 10 to 15 packs during a typical two-hour swim.
Michael Sabala, assistant women's swimming coach at Columbia University, attended a summer training camp with Crippen and wondered if the caffeine, combined with the heat, could have contributed to Crippen's death.
"Elite athletes push themselves to the very edge," he said. "If there is a new edge, they don't know when they are about to fall off."
Open water swimmers keep gel packs in their bathing suits and drink them at intervals during the race. They are also used commonly by marathon runners and cyclists.