Definition: swimming a minimum of 10 kilometers (6.2 miles) in the large outdoor bodies of water such as oceans, bays, lakes, reservoirs, rowing basins and rivers, as defined by FINA (Fédération Internationale de Natation Amateur), or a minimum of 25 kilometers (15.5 miles) as defined by the International Marathon Swimming Hall of Fame.
Also Known As: open water swimming, rough water swimming, long distance swimming
Examples:
The athletes were preparing for a 25-kilometer marathon swimming race.
