On the morning of November 17, Nick Mevoli lay floating on his back in a Bahamian lagoon, taking huge gulps of air in a process known as packing – expanding his lungs 50 percent beyond normal capacity. Mevoli was preparing to dive 236 feet without an oxygen tank, one of 34 divers who'd come from 16 countries to participate in Vertical Blue, an annual free-diving competition. Though he'd taken up the niche sport only a year ago, the 32-year-old was hoping to set his third record.

Those breaths would be among his last. After a three-minute, 36-second plunge, Mevoli surfaced with a look of horror on his face. Within 15 minutes, he was dead.

Carla Sue Hansen, a 55-year-old free-diver and a judge at the competition, was watching from just a foot away. "We've had people do much deeper dives and never have an injury," says Hansen. But, she says, Mevoli's death suggests that the sport's governing body should take a closer look at training and competitive practices. "Clearly, something is wrong."

Free-diving has been around for thousands of years, dating back to ancient Greece and Egypt, but it didn't become a competitive sport until 1949, when Italian pilot Raimondo Bucher plunged 98 feet on a single breath. The fledgling sport attracted self-taught daredevils until it grew big enough to warrant the formation of an international governing body in 1992, known by its French acronym, AIDA. In 1999, it went mainstream when an American newcomer named Brett LeMaster set a world record with a 266-foot dive.

"That's when people realized you don't have to be a genetic freak to do it," says Grant Graves, former president of the American free-diving body, the U.S. Apnea Association (apnea is Greek for "without breath"). Though the sport has no TV coverage and few sponsors, over the past eight years its ranks have roughly tripled; Graves says there are now tens of thousands of free-divers, casual and competitive, worldwide. He attributes this growth to an explosion of free-diving classes and online tutorials in which divers share techniques and training tips. "It's become a generational shift," he says.

A Florida native who had moved to New York City to pursue acting and writing, Mevoli was typical of the daring individualists and spiritual seekers drawn to the sport. He was creative and friendly, a BMX biker and screenwriter who got odd jobs on TV and film sets and let friends couch-surf at his Brooklyn apartment. "Nick was universally liked – sensitive and sweet," says Graves. "But he was a very driven, ambitious athlete."

After he discovered free-diving, Mevoli shifted all his attention to it. He trained in local pools, ran up and down stairs holding his breath, and scrimped to cover travel expenses to competitions. His view of the sport, described in a blog, echoed the quasi-mysticism that grips many of its participants: "Water is acceptance of the unknown, of demons, of emotions, of letting go and allowing yourself to flow freely with it. Come to the water willing to be consumed by it, but also have confidence that your ability will bring you back."

"It is highly transformative," says Graves of the free-diving experience. "You're deep in the water, inside yourself, suspended in silence. It's a powerful mind-body connection."

Though the sport attracts loners, there is also a sense of camaraderie. At events like Vertical Blue, the divers share communal meals and spend downtime spearfishing together. "It's a nice little community on the water for a few days," says Lance Lee Davis, 37, a self-taught free-diver from Los Angeles who holds the world record for underwater somersaults on a single breath (36).

Many divers come to the sport from scuba or spearfishing, looking to shed their gear and feel freer or to get closer to their prey. They enjoy the solitude and the mastery over their biological limits – as well as the awe of onlookers. "It's pretty cool to go underwater for four minutes when your friends are around and see them freak out," says Graves. "It's, pardon the pun, unfathomable to them."

Holding your breath underwater, of course, is a wholly unnatural act. Humans are not meant to do it for very long, or to go very deep. But, according to Graves, anyone is capable of a three-plus-minute breath hold and a 100-foot dive. "I could get you doing that on your first lesson," he says.

The average-size person has a five-liter lung capacity. At rest, you use only the top third of your lungs. But free-diving techniques like packing can teach you, much the way singing lessons can, to pull your diaphragm down and maximize that air capacity. Doctors caution, however, that this process can scar lung tissues, impairing their ability to take in oxygen and expel nitrogen. "We warn people," says Hansen, but even as a judge, she can't stop divers from doing it.

There are other dangers as a diver descends: The water pressure can rupture eardrums and squeeze vital organs; a buildup of nitrogen in the brain can cause debilitating disorientation. While the body has some innate survival mechanisms, divers train obsessively to counteract these effects. Davis rides his bike for long stretches without breathing. He swims 50-meter underwater laps, stops to take five breaths, and repeats until he can't take it anymore (usually three to five laps). "I'll train sometimes until I cry," says Davis. Through all of this, they work on staying relaxed; tense muscles and a rapid heartbeat can eat up precious oxygen.

During Mevoli's dive – which would have set an American record for a plunge without fins – one of these tactics may have gone awry. At 207 feet, sonar monitors showed, he paused and flipped from head-down to head-up; he was likely having trouble equalizing his eardrums, says Graves. After an adjustment, he continued diving, but he paused to flip upright again at 223 feet. He reverted to diving position and followed a line to a weighted plate at 236 feet, the predetermined depth he was aiming for, pulling a tag to prove he'd hit it. Then came the hard part: swimming to the surface on very low oxygen. Mevoli made it back, verbalizing to Hansen that he was OK, as per required procedure, and then took several quick breaths. "Nick did not run out of oxygen," Hansen notes. "He didn't black out."

But moments later, he went into cardiac arrest and died on the diving platform. At press time, Mevoli's autopsy had not been completed, but Hansen speculates that he had an undiagnosed congenital problem or damaged his lungs by pausing on the dive.

In the wake of Mevoli's death, AIDA will be reviewing its rules. For starters, divers currently are not required to get a physical prior to competition. If it turns out Mevoli did have a preexisting condition, "we might need to start requiring chest X-rays," Hansen says.

Graves, meanwhile, says that free-divers need psychological training, too: "Deep things come up in your mind when you're down there. It's very easy to lose focus and lose your way." However, he cautions against heaping blame on Mevoli – or the sport he loved. "Nick was very gifted, and he came on very quick," says Graves. "There are risks in anything – car racing, boxing, football. If you get off the couch and go into the unknown, we are all Nick. He just went deeper than most."