A nonstop open-water swim, undertaken according to standardized rules, and requiring at least several hours of sustained effort to complete. Ten kilometers without significant assistance from currents is the minimum distance considered to be a marathon swim.
Remaining in the water for the entire duration of the swim from start to finish without intentional physical contact with escort vessels, support personnel, or other objects (fixed or floating).
Without artificial assistance to performance, other than the standard equipment of the sport. Any swim that benefits from assistance - in the form of nonstandard performance-enhancing equipment, supportive contact with the swimmer, or other violation of the spirit of unassisted marathon swimming - is considered an Assisted Swim.