Urusei Yatsura: The Shougaibutsu Suieitaikai
Genres: Action, Comedy, Romance, Sci-Fi
Type: Special, Episodes: 1
Aired: Jul 30, 2008
Studio: Sunrise
Source: Manga
Rating: PG-13 - Teens 13 or older
Synopsis:
On a very hot summer day in Tomobiki town, Lum, Ataru, and the rest of the gang are looking forward to using the school's pool. But the teachers have other plans: setting a ludicrous obstacle course between the students in their swimsuits and the pool... naturally this ends in complete chaos.

(Source: AniDB)