Open Water Swimming, by definition, is a swim in any natural body of water including rivers, lakes, or ocean, which usually focuses on long distance and marathon distance swims.

Distances
In open water swimming, athletes compete in lakes, rivers and sea over distances varying from 1.5km to 25km. Open Water World Championships, sanctioned by FINA, are held at distances of 5km and 25km; there are other distances contested, too. And of course, the world of triathlons feature open water swims at the first leg of the race. Distances can vary from the sprint triathlon's short (500 meter) splash to the Ironman distance's long (2.4 mile) soak.

Olympic Event
Open Water swimming will make its Olympic debut at Beijing Games in 2008 after the International Olympic Committee Executive Board agreed the sport for inclusion. The 10k event for both men and women has been given the go-ahead. Open Water swimming was officially recognised by FINA, the world governing body of swimming, in 1986, but you can go back to the 1896 Olympic Games and before to realise that Open Water swimming was the forerunner of the indoor competitive swimming that we know today.