From SF Gate:
"...Ross Ehlinger, 46, an attorney from Austin, died just one minute after jumping into the 51-degree water of San Francisco Bay at the start of the race. Race officials say he suffered a heart attack, but the medical examiner's office has not issued a finding on Ehlinger's cause of death. ..."
There is a gallery of the race there as well.
I am doing the same crossing in May but I suspect the water will be a degree-or-two warmer. Hence my strategy is to swim "doubles" or swim twice each day at Aquatic Park, three-days-in-a-row so as to acclimatize myself to San Francisco bay water. Screw tapering.