The first U.S. swimmer to clinch a berth in the 2012 Olympics, Alex Meyer is heading to London as a teammate of Michael Phelps and Ryan Lochte. But his medal pursuit, as the lone American man to qualify for London’s 10-kilometer marathon swim, will have virtually nothing in common with that of the would-be kings of the pool.

Not even water.

Meyer’s event will be held in Hyde Park’s venerable Serpentine, a lake that King George II created at the request of Queen Caroline in the 1730s. If last year’s test event is any gauge, the water will teem with algae. And it will churn furiously in the wake of 25 competitors’ lashing arms and legs, with untold tugging and shoving beneath the surface.

Marathon swimming is the little-known relative of Olympic pool swimming, having made its Olympic debut at the 2008 Beijing Games.

It’s far less lucrative than traditional Olympic swimming, with no corporate backers to speak of. Meyer barely gets by on his $3,000-a-month stipend from USA Swimming, which is augmented by occasional international prize money.

And it’s far more grueling, contested in lakes and rivers at distances of 10 and 25 kilometers. Only the 10K is contested in the Olympics. In London, the women are expected to complete their Aug. 9 race in just more than two hours; the men’s event, on Aug. 10, should take just less than two hours.

The son of former college swimmers (his father swam at Hobart; his mother at Georgia), Meyer was a two-time all-Ivy League swimmer at Harvard who excelled in the mile, the longest distance contested in college.

But the more he trained, the more he wanted to test the limits of his endurance. He found his outlet in open-water racing, in which the challenge is not to replicate perfection on every lap but to respond to changing conditions over far longer distances.

It’s a jazz riff, in a sense, on pool swimming — demanding improvisation rather than structure.

“Obviously it’s not about the money,” said Meyer, 24, who shares an apartment in Boston and continues to train with Harvard Coach Tim Murphy, his mentor these past six years and also the U.S. Olympic open-water coach. “I just love racing. And I love seeing how much my body can endure.”

At 5 feet 11, 155 pounds, there’s nothing physically imposing about Meyer, who started swimming competitively at 7. Nor did he bristle with raw talent as a Harvard freshman whose specialty was freestyle. Neither mattered to Murphy.

“I don’t get too carried away about talent one way or the other,” Murphy said. “Once you get to school, you’ve got to go to work and do something with it.”

That’s where Meyer distinguished himself in Murphy’s eyes. He relished the hard work of practice. He took pride in the distances he and his teammates logged. And he competed furiously, in and out of the pool.

“The longer the race, the better he was at it,” Murphy said.

Still, not every swimmer who excels in a pool can make the transition to open-water racing.

When Meyer explains the dynamics of an open-water race, it hardly sounds like swimming at all. It incorporates the tactics of cycling, with the front-runners among the pack of 25 creating a draft, or current, that can be helpful to swimmers behind them, allowing them to cruise along while expending less energy. It also involves the contact of wrestling, which isn’t necessarily legal but is commonplace farther back in the pack.

And it demands the strategy of chess. Amid the chaos of an open-water race, that means knowing when to set the pace and when to slip into the draft for a breather; when to grab a water bottle from the feeding poles stationed throughout the course vs. when to motor past and save refueling for later; and when to overtake.

What separates open-water champions from also-rans isn’t impeccable form or a prototypical body type. It’s a combination of factors, most of them mental. Chief among them: a high tolerance for pain; a knack for adapting to changing conditions, whether shifting currents or jostling from competitors; and the ability to stay calm in face of mayhem.

“The mental preparation goes hand in hand with the physical aspect of it,” Murphy said. “A lot of things are going to happen within the context of a race that might be difficult to practice. There’s a lot of banging that goes on. There are elbows and tugs, so you have to be able to handle that and almost expect it because if you don’t, emotionally, you can get upset. And there’s just no time for that because it’s a lot of wasted energy.”

The venue in London will be particularly memorable, with tens of thousands of spectators expected to ring the course. During their six laps around the course, swimmers will be able to glimpse the houses of Parliament. Buckingham Palace isn’t far beyond.

Meyer dreamed of competing alongside his friend Fran Crippen, a University of Virginia graduate and open-water veteran who helped him learn the sport’s nuances as a young competitor. Crippen died in October 2010, at age 26, during an open-water race in the United Arab Emirates in water that was determined to be too hot for distance swimming. Autopsy reports found heat exhaustion partly to blame.

Meyer, the first to notice Crippen hadn’t exited the water, has added his voice to those calling on FINA, the sport’s international governing body, to raise safety standards for open-water events and enforce them. But Crippen’s death, which Meyer considers a freak accident, has not dissuaded him from competing.

“I just felt like the best way I could honor him was by achieving a goal that we both shared,” Meyer said. “That was making the Olympic team.”