Finswimming is an underwater sport consisting of four techniques involving swimming with the use of fins either on the water's surface using a snorkel with either monofins or bifins or underwater with monofin either by holding one's breath or using open circuit scuba diving equipment. Events exist over distances similar to swimming competitions for both swimming pool and open water venues. Competition at world and continental level is organised by the Confédération Mondiale des Activités Subaquatiques (CMAS). The sport's first world championship was held in 1976. It also has been featured at the World Games as a trend sport since 1981 and was demonstrated at the 2015 European Games in June 2015. Rules and description of the sport Competitors are described within the International Rules as 'swimmers' rather than as finswimmers or divers. Classes of competition Competition is divided into 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 Olympic-size swimming pool (also known as a long course pool) is 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. Techniques Surface finswimming Surface finswimming (also known by its acronym, SF) is swimming on the surface of the water using mask, snorkel, and monofins. SF races are held for distances of 50, 100, 200, 400, 800, 1500, 4 × 50 mix relays (2 men's, 2 women's), 4 × 100 relays and 4 × 200 relays (meters) in swimming pools and over various long distances in the open water environment. Swimmers must remain on the surface of the water at all times for the duration of the race except when starting or make a turns at the end of a swimming pool where an immersion over a distance