An otter is a semiaquatic mammal that feeds on fish and shellfish, and also other invertebrates, amphibians, birds and small mammals. Otters have long, slim bodies and relatively short limbs, with webbed paws. Most have sharp claws on their feet and long, muscular tails. The otter ranges in adult size from 2 to 3 ft in length and 3 to 35 lbs in weight. They have very soft, insulated underfur, which is protected by an outer layer of long guard hairs. This traps a layer of air which keeps them dry and warm under water.

Otters build dens with underwater entrances in the banks of streams or lakes. They spend most of their time in water, and when diving are able to close their nostrils and ears. They are most active at night. Otters eat mainly crayfish, frogs, turtles, and fish. They have one to four pups each year. The pups must be taught to swim and do not leave their mothers until they are about one year old. Both adults and young spend hours sliding down river or snow banks into the water.