Amy Martich hit the water at about 7 a.m. Sunday with about 10 to 15 other swimmers ready to take on the Hudson River in the first leg of a popular New York triathlon.
Other contestants dived in right behind them -- one group of after another, each spaced out at 10 to 15 second intervals to avoid the churn of hundreds of swimmers shoving off at the same time, officials said.
Martich, 40, of Elmhurst, Ill., was about halfway through the nearly one-mile long course when she experienced some sort of "massive medical event," said Bill Burke, race director for the Nautica New York City Triathlon.
"The reports from swimmers near her was that they were stroking along, and she was stroking along, then a moment later she wasn't," Burke said.
Martich died early Monday at St. Luke's-Roosevelt Hospital, where she was taken with what police described as heart attack symptoms. A 64-year-old New Jersey man also died, Burke said.
The deaths occurred as triathlons have exploded in popularity across the country and as medical reports have zeroed in on the potential danger of the swimming part of the competitions, which also include running and biking segments.
USA Triathlon, the Colorado Springs, Colo., organization that sanctions more than 3,000 of the events in this country, reports that participation in the sport is at an all-time high. Membership in the organization totaled more than 135,000, the organization stated. Annual membership ranged from 15,000 to 21,000 from 1993-2000, according to the organization's web site.
The event Sunday was the 11th New York Triathlon. The first year, 683 people signed up. By 2010, organizers had to create a lottery for entry due to overwhelming demand, they said in a statement. This year, entrants came from 43 states and 26 countries. Registration for the race filled up in six minutes, they said.
A Minneapolis Heart Institute Foundation study of nearly 960,000 triathlon participants in 2006-2008 found a death rate of 1.5 athletes per 100,000 participants. Researchers determined that about 95 percent of those fatalities occurred in the swimming segment. The researchers also found that deaths were more common in events with greater numbers of participants.
The study looked at 14 triathlon deaths and found that 13 victims were in the water when they either died or started getting into trouble. Autopsies determined that seven had cardiovascular abnormalities, according to the study.
Preliminary results of the study published in the Journal of the American Medical Association last year recommended establishing minimum standards for competing in triathlons, including swimming proficiency.
There was no indication that Martich was hit or injured while in the water, Burke said.
"There wasn't a lot of jostling," he said.
Burke said weather conditions on Sunday were optimal, with relatively mild temperatures and good cloud cover for much of the day.
A staff kayaker watching for medical emergencies jumped out and put Martich on a jet ski, then brought her to the water's edge, where she was given advanced life support before being taken to the hospital in critical condition, Burke said.
Police said 26 others were removed from the water needing assistance for minor injuries or pains throughout the swim.
Burke said there were more than 3,000 participants this year. Athletes in the yearly race also bike 25 miles along Manhattan's West Side highway and finish with a 6-mile run through Central Park.
The participants attended a mandatory briefing before the race that includes information about training and staying hydrated.
During the same triathlon three years ago, a 32-year-old competitor from Argentina was pulled from the water unconscious near the same location. He died after the rescue.
The medical examiner ruled that the man died from hypertensive cardiovascular disease, a condition linked to high blood pressure. Race organizers said he was apparently unaware he had the condition.