Kenkō Zenrakei Suieibu Umishō (ケンコー全裸系水泳部 ウミショー) is a Japanese manga series written and illustrated by Mitsuru Hattori. It was serialized in Kodansha's manga magazine Weekly Shōnen Magazine from July 2005 to April 2008, with its chapters collected in nine volumes. A 13-episode anime television series, produced by Artland and directed by Kōichirō Sōtome, was broadcast from July to September 2007.
Plot
Within the Kanagawa prefecture lies the seaside city of Umineko. There, Kaname Okiura, a student in his second year of high school, attends Prefectural Umineko Commercial High School (県立海猫商業高等学校), or Umishō (海商) for short. He is also the manager of the high school swim team though he himself does not know how to swim. In fact, he is afraid of the water stemming from an incident which occurred some years ago. While he was at the beach, he had nearly drowned when a "mermaid" pulled him under the water. He joined the school's swimming club in order to learn how to swim, but the club is filled with weirdos, who do not teach him swimming.
One day, a floating house arrives at the shores of Umishō bearing two persons. One of these is a cheerful, sunny, happy-go-lucky girl named Amuro Ninagawa, a transfer student, and the other is her father. Her incredible swimming speed makes her an instant hit with the swimming club, but Kaname is surprised, as she reminds him of the mermaid he saw only once in his early childhood. After her floating house is destroyed during a storm she moves to Kaname's house.