Competition is divided in two classes: swimming pool and long distance also called open water.
A swimming pool must be 50 m long by 21 m wide and 1.8 m deep, i.e. an Olympicsize swimming pool also known as a long course pool suitable for the holding of swimming races for either the Olympic Games and a FINA world championships.The International Rules do not permit the use of 25m length pools known as short course although these are used in regional and national competition. Long distance sites include both the sea and natural water bodies such as freshwater rivers and lakes. Site selection criteria include low current and tides and water quality appropriate for swimming as certified by a local authority. The site, when in use for competition, will be marked by buoys, patrolled by safety boats and will have observation points or additional boats for judges to oversee any turns present in the course.