Suijutsu is the name of our water techniques, however, among our traditions there are also other names.
The term used in Togakure-ryu are called suitonjutsu (science of escaping with water; 水遁術) and include techniques and methods to escape and attack by water, i.e. different forms of water with or without transitional means; swimming, flotation, etc., but also swimming in water, with or without arms.
I once showed the swimming method “senpei suieihō” (Folding Fan Swimming Method; 扇平水泳法), a few officers from the Navy’s EOD team in Skredsvik and they recognized it as the way to train in swimming FM … and it’s the same as a Navy SEAL Combat Swim .
In Shinden Fudo ryu (jutaijutsu) the water techniques are called “Suichū shiai no waza” (水中試合の技) and is a part of Okuden Gata. Suichū translates to “under water” and shiai as “fight, match, or competition”.
Water methods in Kukishin-ryu are called “suihō (water methods; 水法) and includes rapids techniques and underwater methods referred to herein as “Suichū katsu jizai-hō” (methods of freely moving underwater; 水中活自在法). There are also methods for when you are with a horse in water called “suiba” (water water; 水馬) and other tactical methods of activity in water.
Hatsumi Sensei has said that “Suiren” (water practice; 水練) is important for the development of good koppojutsu and even wrote about it in the book Sengoku Ninpo Zukan.
Outside of Bujinkan there are 12 known ryuha in Japan engaged in suijutsu. They have a regional character, some focusing on distance swimming, others on the rapids swimming. There is a school exclusively dedicated to the UV techniques, others with different signaling with flags and fans to be worn while swimming. One of the schools claim to have originated among the pirates in southern Japan.
The 12 ryuha are:
Kobori Ryū Tōsuijutsu小堀流踏水術
Mukai Ryū Suihō向井流水法
Nōshima Ryū能島流（äka Nojima Ryū野島流）
Shūme Shinden Ryū主馬神伝流
Suifu Ryū Suijutsu水府流水術 (inkl Suifu Ryū ōta-ha水府流太田派)