FORT LEE, N.J. — An athlete competing in the Ironman U.S. Championship in New York and New Jersey died Saturday after having a medical problem during the swimming portion of the grueling triathlon, race officials said.

The competitor “experienced distress” during a 3.8 kilometre swim in the Hudson River at the start of the all-day competition, a publicist for the race organizers said.

The swimmer was taken to a hospital, but did not survive. The organizers said the cause of death is unknown. An autopsy is planned.

Contestants in the race were following their swim in the Hudson with a 180 kilometre bicycle ride through the suburbs, and then a 42.1 kilometre marathon that was to end at Manhattan’s Riverside Park.

Deaths in triathlon competitions have happened with regularity in recent years, and the Hudson River has been particularly dangerous.

Two people died during the swim portion of the Nautica New York City Triathlon last summer. A male competitor also died during the New York City Triathlon in 2008.

After a spate of five deaths around the country in two months last summer, a governing body for the sport, USA Triathlon, created a task force to examine the fatalities.