Wooper usually live in water but come out onto land seeking food occasionally. On land, they coat their bodies with a gooey, toxic film.
(From  Bulbapedia) Wooper is a mostly blue, amphibious Pokémon that resembles an upright, armless axolotl. Wooper's head is large compared to its body, and it has small, round, black eyes. It has purple, branching gills on either side of its head; the males have more branches in its gills than the females. Wooper stands on two small, round feet, and it has a large, thick tail. On its belly are dark blue curved markings.
It is implied in the anime that Wooper is a dull-witted Pokémon oblivious to its surroundings. Wooper lives in cold water most of the time. When sleeping, it partially buries itself in the mud at the bottom. It will occasionally leave the water when the air cools in the evening to search for food along the shore. While walking on land, it coats its body with a slimy, toxic film that keeps its skin from dehydrating and insulates against the cold. The film causes a shooting pain if touched barehanded.
(From  Bulbapedia) Wooper seems to be based on a larval salamander, which has a flat tail and feathery, external gills. Its Shiny sprite gives it a similar coloration to that of albino, leucistic, and flavistic color mutants, or an axolotl, a species of salamander that keeps its gills and remains in the water for all of its life because it never develops lungs.
(From  Bulbapedia) Wooper and Upah are derived from wooper looper, a marketing term created in Japan that started a pet salamander raising fad. Wooper loopers are the Japanese term for the axolotl, a species of salamander.