Men and women compete over the distances of 5, 10 and 25km while in the team event two males and females per team swim a 4x1250m relay. All events have mass starts and swimmers are required to cover the distances over laps maked by buoys (one lap is usually 2.5km long but based on the local circumstances it can also be 1.25km).
Open water events can only be held in still waters (so rivers or venues with bigger currents are excluded), though depending on the location it can be either sweet or salt water. Practically only the water temperature can be an issue at an event – according to the present day rules it has to be between 16C and 31C at international events (MASTERS 18C and 31C). Race officals can also opt for postponing or cancelling a race in case of high waves too.
Open water races sometimes don’t lack toughness from the competitors who might have body-contacts especially at turns though the rules forbids the swimmers to withhold their rivals by any moves. The most serious offences are punished by yellow cards and in case of committing another fault any swimmer can be disqualified from the race (as it happened at the Rio Olympics where two top athletes lost its respective medals due to alleged illegal moves in the finish).