From Bulbapedia, the community-driven Pokémon encyclopedia.
Maisie Island (Japanese: レフレ島 Refle Island) is an anime-exclusive location in Hoenn found between Lilycove City and Mossdeep City.
It appeared in Clamperl of Wisdom, when Ash and his friends met up with Spoink again.
Isaiah lives on Maisie Island, where he runs his own Clamperl research laboratory, which is complete with a pool enclosure home for several of the Bivalve Pokémon. Many young Trainers like Madeleine also live on the island.
Pokémon seen on and around Maisie Island