Two endurance athletes, including a firefighter, died during the same grueling 70.3-mile half Ironman in Wisconsin, officials said.

Todd Mahoney, 38, a nine-year veteran of the Madison Fire Department, and Michael McCulloch, 61, were both pulled out of Lake Monona on Sunday during the 1.2-mile swim that kicked off the three-section race.

McCullough ? a married father of one ? was pronounced dead on arrival at the hospital. Doctors battled to save father of three Mahoney for 48 hours before he died Tuesday morning.

?My thoughts are with the families and loved ones of the two athletes,? said Madison?s mayor, Satya Rhodes-Conway.

?It is a tragic coincidence that two men died competing in the same event.?

The Ironman 70.3 is a three-part race, with a 1.2-mile swim, 56-mile bike ride and a 13.1-mile run.

?The well-being of our competitors is paramount and we are grateful for the effort and quick support of medical personnel,? Ironman said in a statement to WKOW.

?We will continue to work with the local authorities to gather all the details on these incidents and will continue to do everything possible to provide a safe environment for our athletes.?

A 2016 study found there had been 135 deaths during triathlons between 1985 and 2016, with most during the swimming section.