water rat

Short definition from Wiktionary

Noun

1. 1
   Any of various aquatic or semi-aquatic rodents from Florida and southern Georgia, especially Neofiber alleni; the muskrat.
2. 2
   A water mouse, especially, the rakali, Hydromys chrysogaster.
3. 3
   A European water vole (Arvicola amphibius, formerly Arvicola terrestris).
4. 4
   A petty thief or waterfront ruffian.
5. 5
   A person fond of water sports.
6. 6
   A member of the water police.
7. 7
   Alternative form of water rat.