It has a flotation sac that is like an inflatable collar. It floats on water with its head out.
Biology
Physiology
(From Bulbapedia)
Buizel is an orange Pokémon resembling a weasel and a sea otter. It has a yellow collar around its neck that functions as a flotation sac. It has two blue fins on its arms and a tail, which appears to be split, that resembles a fish's fin. There are parallel marks on their cheeks. Additionally, Buizel has cream paw pads on its feet.
Gender Differences
Male Buizel have two cream spots on their back, while the females only have one.
Special abilities
The yellow collar that surrounds its neck can be inflated and used as a flotation device when it inhales. By inflating this sac, it can keep its face above water to watch for prey movement. Its tail also acts as a boat propeller by spinning.
Behavior
Habitat
It is most likely found in or near swift-moving rivers. Though it is unknown what diet Buizel follows, it was shown in the anime eating Oran Berries.