of 15m is permitted. Apnoea finswimming Apnoea finswimming (also known by its acronym, AP, and as apnoea or apnea) is underwater swimming in a swimming pool using a mask, monofin and holding one's breath. AP races are held for the distance of 50m. A swimmer's face must be immersed for the duration of the race otherwise he/she risks disqualification. AP races are not conducted in open water for 'safety and security reasons'. Immersion finswimming with breathing apparatus Immersion finswimming with breathing apparatus (also known by its acronym, IM, and as immersion) is underwater swimming using mask, monofin and underwater breathing apparatus conducted in a swimming pool. While there are no requirements on how a breathing apparatus is carried, it cannot be exchanged or abandoned during a race. IM races are held for distances of 100 and 400 m. A swimmer's face must be immersed for the duration of the race or risk disqualification. IM races are not conducted in open water for 'safety and security reasons'. Historically, IM swims were conducted in open water up to distances of 1000m. Bi-fins Bi-fins (also known by its acronym, BF or as 'stereo-fins') is swimming on the surface of the water with mask, snorkel and a pair of fins using a crawl style. BF races are held for distances of 50, 100, 200, 400 and 4 × 100 mix relays (2 men's, 2 women's) in swimming pools and over various long distances in the open water environment such as 4 km and 6 km. It is reported that BF was introduced in 2006 to provide the opportunity for competition by swimmers who cannot afford to purchase a set of monofins. 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 of a distance of 15m is permitted. Equipment Finswimming which is often compared to sports swimming differs from that sport in the use of masks, fins, snorkels and underwater breathing apparatus. This reflects the sport's origins in the underwater diving techniques of snorkelling, breath-hold diving and open circuit scuba diving. Apart from requiring the use of a mask for protection of the eyes and for the ability to see underwater, the international rules have no requirements regarding selection. Centre-mounted snorkels (also known as front snorkels) are the only