First you have to define what constitutes a swim. Most experts, including cold-water distance swimmers Lynne Cox, 54, and Lewis Gordon Pugh, 41, play by English Channel (EC) rules, which require you to start and end on land, allow the use of a swim cap, goggles, and a bathing suit (but no wetsuit, flippers, or shark cage), and permit a boat crew to feed and hydrate you. But you can't rest by hanging off the side of a craft or sleeping on it, a luxury that some distance swimmers allow themselves.
Indeed, sleep deprivation might be the biggest barrier. The longest known duration for an open-water swim is Canadian Vicki Keith's two-way crossing of Lake Ontario in 1987, a distance of 64.6 miles that took her 56 hours and 10 minutes. Diana Nyad holds the title for pure distance, with her 102.5-mile swim from North Bimini, Bahamas, to Juno Beach, Florida, in 1972. But Tim Johnson, author of History of Open-Water Marathon Swimming, says a fast current gave Nyad a major boost. Using EC rules, he says, "we're not going to see anything much longer than 60 miles unless you're utilizing currents."
Swimmers Jon Erikson, Philip Rush, and Alison Streeter are the only people to complete a three-way crossing of the English Channel, a 63-mile haul. Is anyone crazy enough to go for four? "I wouldn't even want to be on the boat to witness that kind of suffering," says Johnson.