Kim Sung-won, 40, was knocked off his jet ski when it hit high waves while entering the first curve of the tournament's Pro-Am Endurance Open event.
A rescue team took Kim – a member of the Freedom Racing Jet Ski Team – to shore and attempted to revive him. He was subsequently sent to Bangkok Hospital Pattaya where he was pronounced dead.
Doctors said they believe he died of asphyxiation.
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