From Bulbapedia, the community-driven Pokémon encyclopedia.
Blue Point Isle (Japanese: 青岩島 Seigan Isle) is an anime-exclusive location in Johto, and the largest island in the Whirl Islands archipelago. Known as the entryway to the Whirl Islands, it is located northeast of Cianwood City. Ancient seamen named it for the large blue rock near Inland City that guided them safely home.
Trainers who specialize in Water-type Pokémon can register for the Whirl Cup on Blue Point Isle.