Immersion swimming with breathing

Immersion swimming 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 swimmers 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 openwater up to distances of 1000m.