A naval officer attached to the Air and Coastal Defence Command passed out while taking part in a swimming competition at the Sattahip naval base in Chon Buri and died later at a hospital on Sunday morning, the navy announced.
The officer was identified as Cdr Somphan Meethong, 53, chief of a training battalion of the Air and Coastal Defence Command.
Cdr Somphan became unconscious at about 7.35am during the swimming competition, which is part of the ongoing triathlon of the navy. He was immediately helped out of the water by an emergency medical evacuation team on a jet ski.
The officer was admitted to Queen Sirikit Naval Hospital, where he was pronounced dead at 11.11am.
All of the athletes taking part in the navy's triathlon had life insurance coverage by Thaivivat Insurance Plc. An athlete who dies is entitled to a 500,000-baht payout.
According to the navy's announcement, Cdr Somphan was healthy and regularly had fitness training as he was an athlete of the Air and Coastal Defence Command in triathlon.
The cause of death was believed to be acute heart failure, which could happen even to people who are declared healthy and strong, said the announcement.
Adm Luechai Ruddit, the navy commander, said that despite the incident, the navy triathlon will continue.