Senkaji Choo (Chinese: Zhang Heng) is a fictional character in Water Margin (Suikoden). Nicknamed "Boatman", he ranks 28th among the 36 Heavenly Spirits, the first third of the 108 Stars of Destiny.
Senkaji is described as an excellent swimmer, he can propel himself in water like a flying fish.He is nicknamed "Boatman" for his prowess in the water. Even harsh weather conditions cannot deter him. He is the older brother of Rorihakucho Chojun (Suimonyaburi).

After living as fishmongers and ferrymen, the brothers join the Suikoden outlaws and become commanders among the outlaws' fleet of ships. During the Suikoden's campaign against Hourou's (Chinese: Fang La's) rebel forces, Senkaji's younger brother, Chojun, tries to sneak into the Hangzhou stronghold by climbing over the Yongjin Gate. However, Hourou's son and heir, Houtentei (Chinese: Fang Tianding) spots him and orders his archers to kill him. After his death, Chojun's spirit possesses his brother's body and later kills Houtentei (in this tattoo Houtentei is replaced by a dragon) in revenge. Senkaji then becomes unconscious after his brother's spirit leaves his body. When he comes to, he feels so deeply saddened by his brother's death that he falls sick and dies not long later.