At the Olympics, the 10k marathon swim is just another swimming event, like the 400-meter individual medley or the 200m breaststroke. It is not a different sport. Alex Meyer, the lone American man who will compete in the open-water race at the 2012 Summer Games in London, will be a member of the same U.S. swim team as Michael Phelps, and what Meyer does bears some resemblance to what Phelps does. For instance, he crawls through water.

What you see when you watch Meyer, though, is not what you see when you watch Phelps. When Phelps swims freestyle, you can see the way his long body slips through the water: the stillness of his head, the smooth rotation of his shoulders and hips around the axis of his core, and his massive kick, which lets him turn over his powerful arms with a deceptively languid grace. You can see all this because pool water is transparent, and Phelps is politely cordoned off from the other swimmers. Phelps is a calibrated machine, precise and efficient, swimming in a pool designed with swimmers in mind, designed for speed.

When you watch Meyer swim his event, you are basically watching a roller derby in open water. The swimmers surge forward, their heads high and their broad backs riding up, their legs lost beneath the dark surface and the whitewater of their wake. They practically kick each other in the face. It is a mess. They deal with waves, fast currents, sea creatures, seaweed, slime, and the flying feet and elbows of their competitors. At the world championships a few years ago, swimmers had to pass through a massive swarm of stinging jellyfish — as if the swimmers weren’t already hurting badly enough from the sheer distance. Ten kilometers is 200 lengths of a standard international pool, and 400 of the short-course pool that most summer swim club teams normally use. A 25k race (15.5 miles), which Meyer also swims (but which is not an Olympic event), takes the top swimmers about five and a half hours to complete. Miraculously, after such a long distance, there’s often a sprint at the end.

A pool swimmer excels because of his mechanics. An open-water racer needs something else. He succeeds only if he can withstand tremendous pain. Meyer insists that he is not a finely tuned machine, not a freakishly good athlete — a world champion, yes, a member of the 2012 Olympic team, yes, but not a phenom, not a person born with preternatural talent. What he has is endurance. Sitting at his kitchen table in Cambridge, Massachusetts, on a grim day in late February, Meyer tried to describe what it’s like to be in agony in the water. “There’s a feeling like there’s a fire burning you up from the inside, but it’s also a cold fire,” he said. “You’re nauseous, you feel like you’re ready to shit yourself, basically. My fingers and toes start to go numb, my lips — I can’t feel my lips. It’s hard to explain, but it’s a special place. It gets worse and worse and worse up to a certain point, when you cross a threshold, and on the other side, it’s just pure euphoria.”

Meyer spoke in a monotone with his eyes halfway closed. There seemed something catlike about him, something either guarded or sleepy. He held a mug of coffee. His face was impassive, despite the intensity of what he was saying. That euphoria, for instance, is complicated. “You’re still having those same sensations” — the numbness, the burning, the desire to shit yourself — “but you like it. You’re almost getting off to that. You want more and more.”

Meyer used to race in pools, and he did it well. He finished 34th in the 1,500-meter freestyle at the Olympic trials in 2008 and was an NCAA All-American. That’s where he thought it would end. Before his senior year at Harvard, though, he went to the open-water nationals at the suggestion of his coach, Tim Murphy. (Murphy had long been involved in the open-water swimming community and sometimes encouraged his distance swimmers to try it.) Meyer learned the rules of the race and some tactics at a training camp a few days before his first-ever 10k. It was mostly a lark — until he finished fourth, which qualified him for the national team. He ditched his plans for summer school and headed to the world championships in Rome.

There, Meyer swam the 25k. Imagine a runner accustomed only to the track suddenly running a marathon — and then an ultra-marathon a couple of months later. But Meyer has always been able to swim sets that others couldn’t, and he liked the challenge of open-water racing. He quickly discovered that he thrived in unpredictable conditions. He liked the roughness of the race. “I secretly kind of always wished that I did a contact sport,” he admits. In Rome, though, he might have gotten a little too physical. Just before the finish, he ran over a girl, received his second warning, and was disqualified. He was pissed at the officials’ ruling and is clearly still pissed, from the sound of his voice when he talks about it now.

That result was disappointing, but Meyer was encouraged. He had never trained for open-water swimming before, after all, and until he started training, he wouldn’t be able to truly test his limits. For starters, he had to get out of the swim lanes. Back in Boston, to train away from the perfect conditions of the pool, he tried swimming at Nantasket Beach, but it was unbearably cold. Then he remembered a bike ride he and a friend had taken to Walden Pond. He has trained there ever since, with Murphy — “the mastermind, the guru,” Meyer calls him — paddling along in a kayak. Thoreau’s old haunt is a nice place to train. It’s romantic, the woods and the lake, the associations with that famous meditation on rugged self-reliance and individualism. But open-water races aren’t swum alone. They’re swum in a scrum, and you can only learn how to negotiate the scrum by getting inside of it. It also helps to have teammates. Meyer’s regular roommate on the open-water circuit, a swimmer named Fran Crippen, quickly became his friend and training partner, someone he looked up to and looked to for guidance. They shared an attitude that was well suited to open-water swimming. It was a mix of devotion and discipline.

Crippen was nearly four years older than Meyer and, by then, already a top open-water swimmer. At the 2009 world championships, he finished third in the Olympic-distance 10k. At 6-foot-2, he looked the part of a world-class swimmer, more than Meyer, who, at 5-foot-11 and 155 pounds, doesn’t exactly have the physical profile of Ryan Lochte. After a stellar career in the pool at the University of Virginia, Crippen had decided to focus on open-water events. (The 10k marathon swim was added to the Olympics for the first time in 2008.) He came from a family that had a big presence in the sport; his three sisters were also elite swimmers. Crippen was well liked, known to be generous and kind. At the Pan Pacific Championships, Meyer was feeling sick and straggling. Crippen turned back to swim with him. Meyer ended up pulling out, but Crippen won silver, despite time he’d lost checking on Meyer. During an interview with USA Swimming, his sister Teresa remembered watching her brother turn back during the race with disbelief — but also understanding. “Alex was like a brother at that point,” she said.

Crippen was also a ferocious competitor, though. “He was always better than me,” Meyer said, “so it was probably better for me than for him, training-wise, since he was someone for me to look up to.” At the 2010 national championships, Meyer was at the front of the lead pack, closing on the finish, when Crippen ripped by him to win. Later that summer, Meyer won the 25k at the world championships, and he started thinking about the Olympics. He suspected that Crippen would have a good chance to make the 2012 Olympic team, but it was possible for two American swimmers to qualify, and Meyer wanted to be the other one.

Crippen died on October 23, 2010, when he drowned during a race swum in extremely hot conditions. The following summer, Meyer won the national 10k title and, when he finished fourth in the 10k at the world championships in Shanghai, became the first American athlete to qualify for the 2012 Olympics. Meyer talks about Crippen like a phantom member of the Olympic team, and he takes a photo of Crippen with him to meets. “You don’t have to feel awkward about asking me about him,” he said gently when I hesitated the first time we spoke. “I like talking about him.” Meyer is quick to acknowledge that the pain from Crippen’s death has to be worse for Crippen’s family and girlfriend, but the pain was bad enough for him. After Crippen’s death, Meyer spent hours just watching the videos the two had made on a flipcam. Most of them are goofy: a trip on a rickshaw, or fish flopping on blocks of ice in an outdoor market, or various pranks and bets. In late February, Meyer watched some of the videos again for the first time in a while. In one of them, Crippen just rolled and howled with laughter on his hotel bed. “His laugh is pretty incredible,” Meyer said, distracted, and then fell silent. On his laptop screen, Crippen was still cackling. “So, we had some good times,” Meyer finally said.

For Meyer, Crippen’s death made a lonely sport lonelier. “It’s been hard to start going on these trips on the open-water team without him as my roommate,” Meyer said last winter. “I don’t know. The whole dynamic has changed. Honestly, it’s not as fun anymore.”

He caught himself quickly. “I mean, I wouldn’t say that. But it’s definitely changed.”

On a rainy night this past January, Meyer was riding his bike home when his chain caught and jammed. The bike skidded on the slick surface and Meyer fell, hitting his head and his shoulder. A broken collarbone required a screw and four sutures around the bone. By the end of February, after more than a month of physical therapy, Meyer was able to raise his arm above his head. “Not bad,” he said after showing off his progress. I couldn’t tell whether he was serious. His coach, Tim Murphy — who is also the Olympic coach — was not exactly happy with his swimmer. Every day Meyer walked onto the pool deck to ride the stationary, “it looked like [Murphy] wanted to punch me in the face that much more.”

But Meyer shrugged off the concern — or would have, if he could shrug. “I’m not worried about it,” he insisted, and then pointed out that during the winter before he won the 25k at the world championships, he had broken his back. That was much worse. “So, whatever,” he said, his tone flat and clipped. Whatever “whatever” means. By April, Meyer was racing again, finishing 10th at nationals. It wasn’t the ideal result going into the Olympics, but things don’t always go the way you want.

In February, at least, Meyer seemed genuinely proud of the long scar that ran along his collarbone, fresh and flaming. He showed me the pictures he took of himself each day after the accident to show the worsening bruises. In all the photos he had the same sleepy-yet-serious expression, except in the last one, in which he made a face right out of Beavis and Butt-Head. His lack of coordination, on land at least, is a point of satisfaction. As a kid he stunk at tee-ball. Mostly to avoid the babysitter, he likes to say, he joined a swim team. (This is partly protesting too much: Both of his parents were college swimmers.) The pool disciplined him: He set goals, got serious, calculated split times, and shaved his body hair.

Meyer did swim a few open-water races growing up. He liked to listen to his coach tell stories about a girl who had swum 38 miles across Cayuga Lake in upstate New York. “I thought that was the most badass thing ever,” he says. But he didn’t want to do the kind of daring stunts that most people associate with open-water swimming, like swimming among icebergs or to Cuba. “I have no interest right now in, like, swimming the English Channel,” Meyer says. He wanted to race, and he wanted to race where the stakes seemed high. That meant sticking to the pool. In high school, he won two New York State championships in the 500 meters. In college, he excelled in the longest race, the 1,650-meter freestyle, a mile. He also excelled at shorter distances: He qualified for the 2008 Olympic Team trials in the 400-meter freestyle as well as the 1,500. But he was usually slow at the start and had something left at the end. His body has an extraordinary ability — even among top distance swimmers — to withstand the stress and fatigue and to recover from extreme distances. Plus, he has an unusual capacity to tolerate pain. He’s a little crazy. “If you look at all the best endurance athletes there have ever been, they’re nuts,” he said. “Lance Armstrong? That guy is just wacko. That switch, not-worth-the-pain — that wire’s not connected. You embrace pain.”

That’s the race you can’t watch, the race inside his head, the race in which the swimmers try to outlast the torture, to stay just a few strokes ahead of the numbness, the nausea, the shit, riding the pain like it’s ecstasy long enough to near the finish, at which point they’ll ask their bodies to do what seems impossible, to sprint. The race you can see at the Olympics — 30 men swimming six laps of the 1.67-kilometer course in the Serpentine in Hyde Park, right in central London — will be exciting. But the psychological race is just as thrilling. “There is something mental there,” says Meyer’s former teammate John Cole, who has also swum a few open-water races. “It’s willpower over anything.”

So how do you know when your body tells you that you really need to stop? “I think that’s the whole point,” he said. “We don’t stop. Fran didn’t stop. We’re just trained — it goes against the very essence of who we are as people, and as athletes, to quit or stop or give up.”

Meyer wanted to swim at the final World Cup of 2010, in the United Arab Emirates, but he was recovering from an appendectomy. He still almost swam. “I went thinking, I’ll try to be a hero and swim the race,” he remembers. But in the end he wasn’t up to it, and so instead he told Crippen that he’d film his finish. When the first men came in, he expected to see Crippen among them. “You can hear me on the video,” he says. “After the first pack came in, I was like, ‘What? Where’s Fran? This is weird — what’s going on?'” He figured that Crippen might have been disqualified. Maybe he was having a bad race. After all, the day was so hot that Meyer could hardly stand to be outside. Before long, though, Meyer started to tell others he was worried.

Racers who had just emerged from the water dove back in to look for the missing swimmer, and Meyer joined them in the uncomfortably hot water. It took nearly two hours for professional rescuers to arrive. They found Crippen’s drowned body about 500 meters from the finish. No one had seen him go under.

“That was a situation that was just not handled properly by the event,” Meyer’s coach, Murphy, says, anger still edging his voice more than a year later. Two American female swimmers had to get medical attention after the race; one of them had actually felt so ill during the race that she summoned help, but there was no response. Marathon swimming is only dangerous “if it’s not organized in a way to make it safe,” Meyer insists, and others in the swimming community agree. In the aftermath of Crippen’s death, swimmers and officials have emphasized the importance of proper precautions, examining emergency response protocols and issuing recommendations for what water temperatures are considered unsafe. Crippen’s family started the Fran Crippen Elevation Foundation to help protect athletes in the water.

But when I mentioned implementation of new rules and practices during races to Meyer, he bristled. “What rules?” Last July in Shanghai, the water hovered around the upper boundary of the recommendations and above what many athletes considered safe. It was a huge event; the top 10 finishers in the 10k would qualify for the 15-man Olympic field. Meyer swam, and his result put him on the Olympic team. But when temperatures on the morning of the 25k, in which Meyer was the defending world champion, neared 88 degrees — FINA’s recommended cutoff temperature — he pulled out. He was furious that the race was still being held. “It was like” — his voice dropped to a livid whisper — “what the fuck are you guys doing?” Other top swimmers, including the women’s defending 25k champion, Linsy Heister, and former world champion Thomas Lurz, also refused to swim to protect their safety and in protest. When the temperatures pushed the 88-degree marker mid-race, some swimmers who’d chosen to compete assumed the race would be called. But FINA treats the temperature cutoff as a guideline, not a rule, and it chose to continue the event. Two-time world champion Valerio Cleri was among those who had to be pulled from the water. Crippen was on everyone’s mind.

Even in the safest waters — and the Serpentine is among them, cool and calm — the swimmers fight as if survival is at stake. If they stop struggling, if they give in to their bodies’ desires to relax and rest, then they lose. “There’s so much time to think during these races,” Meyer said. “That natural tug of war between fight or flight is constantly going back and forth. It only takes once for the ‘flight’ to win, and you’re out.”