From Bulbapedia, the community-driven Pokémon encyclopedia.
Lakes are large bodies of fresh water that can be found thoughout the Pokémon world. They are often home to Water-type Pokémon, who live in the water, and Pokémon of various other types, who live at the water's edge. Lakes appear in the core series regions of Johto, Sinnoh, and Alola, but smaller bodies of fresh water appear in all regions. They are relatively uncommon, appearing less often than other environments such as forests and caves.
List of lakes in the Pokémon world
In the core series