From Bulbapedia, the community-driven Pokémon encyclopedia.
The Waterworks (Japanese: ちかすいどう Underground Waterworks) is the location of the third mission in Pokémon Ranger. It is the sewage system of Fall City.
A number of Grimer appear in the Waterworks. As the Fall City rangers are investigating the Go-Rock Squad, the player is recruited to capture and remove them. Later, it is revealed that the Go-Rock Squad brought the Grimer from another region, and released them so they couldn't return to their natural habitats. After some consideration, they are allowed to live in the sludge-storage area of the waterways. There was also a Muk that the Go-Rock Squad released as the boss Pokémon.
This is a listing of the Pokémon found in the Waterworks: