From Bulbapedia, the community-driven Pokémon encyclopedia.
A Swimmer is a type of Pokémon trainer that first debuted in the Generation I games. Originally, they only came in male versions, Swimmer♂ (Japanese: かいパンやろう Swimsuit Guy), but in Generation II, female swimmers, Swimmer♀ (Japanese: ビキニのおねえさん Bikini Lady) were introduced.
They specialize in Template:Type2 Pokémon. In Pokemon Stadium, the nicknames of the Male Swimmer's Pokemon end with "mer."
The Japanese versions show the male Swimmers wearing Speedo. This was changed to shorts in the dubs.