(CNN) -- Two men died following an Ironman 70.3 triathlon in Madison, Wisconsin, over the weekend, the Madison Fire Department said.

Todd Mahoney, 38, an apparatus engineer with the fire department, and Michael McCulloch, 61, of Cottage Grove, Wisconsin, both died during the swimming portion of the lengthy race.

The Ironman 70.3, also known as a "half Ironman," is a three-part race, with a 1.2-mile swim, 56-mile bike ride and a 13.1-mile run. A "full Ironman" consists of a 2.4-mile swim, a 112-mile bike ride and a marathon 26.22-mile run.

Two die during Ironman

Mike McCulloch, left, and Todd Mahoney died while competing Sunday in an Ironman triathlon.

Competitors began swimming in heats, starting at 7 a.m. Sunday, according to the Ironman website.

McCulloch was rescued from Lake Monona by the Madison Fire Department, taken to the hospital and later pronounced dead, a fire department statement said.

According to an obituary, McCulloch was a native of the area, and survived by his wife and daughter.

The fire department said it also rescued Mahoney when he was found unresponsive in the lake. He was transported to a hospital, where he died Tuesday.

Mahoney was a nine-year veteran of the fire department and occasionally was an aide to the chief. He is survived by his wife and three young sons, the department said.

The Dane County medical examiner's office told CNN affiliate WKOW that McCulloch's death "was consistent with an accidental drowning due in part to a medical event." The office continues to investigate Mahoney's cause of death, the fire department said.

"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 Sunday 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. In respect of the families and athletes' privacy, we will have no further comment at this time."

Ironman didn't immediately respond to CNN's request for comment.

Madison Mayor Satya Rhodes-Conway issued a statement Tuesday on the men's deaths.

"My thoughts are with the families and loved ones of the two athletes who died while competing in the Half Iron Man on Sunday," Rhodes-Conway said. "It is a tragic coincidence that two men died competing in the same event."

CNN's Sheena Jones contributed to this report.

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