Marathon swimming is one of the most intense and athletically challenging sports in the world, in which competitors swim over 6.2 miles at a time. In the Olympic Games, contestants swim 6.2 miles in their marathon swim, which takes elite swimmers the same amount of time to swim the entire marathon as it does elite runners to finish an entire on-land marathon. Other marathon swimming competitions can be as long as or longer than 30 miles.
Marathon swims are too long to take place in regular swimming pools, so they are held in open bodies of water. Races begin when the swimmer enters the water from land, but end once they can no longer swim in the shallow water closest to the shore.
Swimmers are only allowed to wear bathing suits, goggles, nose clips, and bathing caps and are not allowed to have assistance from any floating devices or escort vessels that follow the competitors. Bodysuits are not allowed in most competitions, as they can increase swimming speed and keep some competitors warmer than those not wearing them.
Swimmers cannot ride directly behind or next to a vehicle running in the water in order to prevent any unfair advantages.
If a swimmer is in poor physical condition, they can be assisted by the escort vessel and pulled from the water to the shore. The competitor forfeits the race as a result.
Because marathon swims take place in open water, swimmers face obstacles like sharks, jellyfish, and large waves that make the swims much more difficult and dangerous. Competitors are not allowed to make purposeful contact with each other, but this is not easily enforceable.