Marathon swimming is a class of open water swimming defined by long distances (at least 10 kilometers (6.21 mi)) and traditional rules based in English Channel swimming. Unlike marathon foot-races which have a specifically defined distance, marathon swims vary in distance. However, one commonly used minimum definition is 10 kilometers (6.21 miles), the distance of the marathon swimming event at the Olympic Games.
As in all open water swimming, tides, surface currents and wind-chop are major determinants of finish-times. For a given course, these factors can vary dramatically from day to day, making any attempt to draw conclusions about athletic ability by comparing finish times from performances undertaken on different days meaningless.
One of the earliest marathon swims was accomplished in 1875 by Captain Matthew Webb, when he became the first person to swim across the English Channel. Similarly, perhaps the most famous marathon swim of all time was accomplished in 1926 by Gertrude Ederle, when she became, at 19 years of age, the first woman to swim across the English Channel. In doing so, she demolished the existing world record for the crossing, by employing the crawl stroke technique.
The Triple Crown of Open Water Swimming includes three of the best-known marathon swims: (1) 21 mi (34 kilometers) across the English Channel, (2) 20.1 mi (32.3 kilometers) between Catalina Island and the mainland in Southern California, USA, and (3) 28.5 mi (45.9 kilometers) around Manhattan Island in New York City, USA.
The Ocean's seven is a collection of seven channel swims: (1) North Channel between Ireland and Scotland, (2) Cook Strait between the North and South Islands of New Zealand, (3) Molokai Channel between Oahu and Molokai Islands in Hawaii, (4) English Channel between England and France, (5) Catalina Channel between Santa Catalina Island and Southern California, (6) Tsugaru Strait between the islands of Honshu and Hokkaido in Japan, and (7) Strait of Gibraltar between Europe and Africa. Irish swimmer Steve Redmond became the first person to complete the Ocean's seven upon completing the Tsugaru Strait on May 15, 2012.