Few sports are as demanding as open water swimming, and even fewer put its practitioners face to face with alpha predators, namely man-eating sharks. For the toughest swims, however, the athletes at the top of this game continue to add danger and difficulty as they strive for ever-more-challenging records. The swimmers below have dived into high-altitude Himalayan lakes, chilled Cold War tensions and braved waters infested with sharks, leopard seals and box jellyfish.

Here are the most epic open water swims ever undertaken.

Trans-Atlantic Fright

The greatest feat in open water swimming is underway right now. It began in May, when Frenchman-turned-Texan Ben Lecomte pushed off into the water near Tokyo, Japan. He is headed for San Francisco. If he completes the 6-month swim across the Pacific Ocean, he will be the first to make this gigantic crossing — the longest open water swim ever. He will use GPS markers to pinpoint the place he stops swimming one day and should begin the next.

A quick look at Lecomte’s resume gives an idea of his chances. In 1998, he swam across the Atlantic Ocean, becoming the first to do so without a kickboard (apparently, some 3-year old had kickboarded his way across the ocean beforehand). He swam eight hours a day, often shadowed by behemoth sharks, on that 73-day mission. He also figured out a nifty trick for upping motivation: before embarking, he asked his girlfriend to marry him. She said that she would tell him her answer in France. He finished the swim… and they got hitched.

Open Water Everest

The highest distance swim was completed at an elevation most people, including lots of mountaineers, never reach. For this record-setting achievement, Lewis Pugh, a British Lawyer and environmentalist, chose Lake Pumori, an alpine lake in the Himalaya Mountains located 5,300 meters above sea level. Mount Everest’s summit is visible from its icy waters. In 2010, Pugh swam a kilometer in this lake. The altitude was an added difficulty, even for Pugh, who was the first person to complete a major distance swim in each of the world’s oceans, including the Arctic and Southern oceans. He swam across the North Pole (yep, you read that correctly) and did a kilometer in Antarctica, the most southerly swim ever.

102 Miles

102 miles: that is the longest that any person has ever swam in open waters, unassisted, without resting. It is a record still standing 30 years after Diana Nyad chopped her way from the Bahamas to Florida. Last year, the sportscaster and squash player attempted to best her own record with a swim from Cuba to Florida, a more difficult stretch of water that is longer by a half mile. As always, she was stung by jellyfish and risked shark attack, as she swam without a shark cage, which is believed to gently pull the swimmer along. After 90 miles and 29 hours in the water, asthma and shoulder pain forced her to give up. Other swimmers have done longer crossings inside cages, but Nyad’s 102-mile swim remains the benchmark for pure, unassisted athleticism in open water.

Cold War, Cold Swim

When Lynne Cox swam across the Bering Strait in 1987, she may have done more than become the first person to splash across the frigid channel. She could have helped thaw Cold War tensions between the U.S. and Soviet Union. When the Soviets granted her permission to stand on Big Diomede, the island that marks the Russian side of the strait, she was the first American in decades given the privilege. Big Diomede and its American cousin Little Diomede are two volcanic nubs between the Chukchi and Bering seas. Between them is an international date line and 2.7 miles of ferocious waters. The nations on each side of the strait smiled on the achievement of swimming between them, apparently for long enough to forget about the constant threat of mutually assured destruction.

Extreme Repeats

Are your swims lacking sparks after all these years? Do you yearn for the days when swimming excited you, made you feel like it was your first time crossing the English Channel? Yeah, swimming the channel, still one of the world’s most hardcore swims, done by fewer people than have climbed Mount Everest,  can get a little dull. When that happens, spice up your swims with some repeats. That’s what Jon Erikson, Philip Rush, and Alison Streeter have done. They are the only people to have swam the channel, turned around, swam it a second time, turned around and done it a third time. The unpredictable weather, currents and shipping boats that frequent the channel make for a zesty, rejuvenating challenge. It’s sure to get your blood pumping, like your first time on the channel all over again.