Wooper is a mostly blue amphibious Pokémon that bears a resemblance to a real-life salamander known as an axolotl. Wooper stands upright on its small, round feet, and has a large, thick tail. Wooper also has purple-colored, branching gills coming out of the sides of its head, and what look like dark blue, curved gill-like markings on its torso. Wooper's head is large compared to its body, its mouth is wide and its eyes are small, round, and black in coloration.
Wooper tend to be dull-witted Pokémon as implied in Trouble in Big Town. They tend to be oblivious to their surroundings. They also share this trait with their evolution Quagsire. Wooper lives in cold water most of the time, but it will on occasion leave the water to search for food when the temperature cools in the evening. While walking on land, it coats its body with a slimy, toxic film that keeps its skin from dehydrating and insulates itself against the cold. In the water, Wooper partially buries itself in the mud at the bottom to sleep.
The film covering Wooper's body when it walks on land is poisonous, and can cause a shooting pain if touched barehanded. Wooper live in cold, clean water, but will occasionally travel over the land in evening in search of food. Female Wooper have smaller gills on the sides of their heads.