A Westchester County man participating in a Suffolk County triathlon died Sunday morning after a lifeguard had to rescue him from the water during the event, police said.

Vincent Fleck, 69, of Mount Kisco, was taking part in the 500-meter swim portion of the Smith Point Sprint Triathlon in Narrow Bay when a lifeguard noticed the man was “in distress” about 7:25 a.m. Sunday, according to Suffolk police.

The lifeguard transported Fleck in a canoe to the Mastic Beach Fire Department rescue boat, and an EMT began emergency first aid, police said. Fleck was transported by Mastic Beach Ambulance Company to Brookhaven Memorial Hospital Medical Center in East Patchogue, where he was pronounced dead, police said.

The cause of death is pending an autopsy by the Suffolk County medical examiner, police said.

Fleck’s relatives could not be reached Sunday.

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The Smith Point Triathlon starts at Smith Point County Park in Shirley with a 500-meter swim in the Narrow Bay and continues with a 16-kilometer bike ride over the Smith Point Bridge to Wertheim National Wildlife Refuge and back, according to the event’s website. The triathlon ends with a 5-kilometer run.

Vicki Ventura of EventPower, which organizes triathlons on Long Island, said in an email that “all measures were taken to ensure that the athletes’ safety was a priority during the entire triathlon event.”

“Our deepest condolences are with the family as we all carry a heavy heart with the tragedy of the passing of the participant in the swim leg of today’s triathlon,” Ventura wrote.