The common otter of Europe is much like the otter inhabiting North America, though the European variety is smaller. Both are superb swimmers. An otter is said to travel in water at a rate of some 10 miles (16 kilometres) per hour. Usually three humps are seen above water when the animal is swimming—the head, the back and the end of the tail. A family group of otters swimming in line has at times been mistaken for a sea monster.

Both the North American and the European otters are also at home on land. Despite short legs, otters can overtake a running man. They may travel some 15 miles (24 kilometres) during a night. There is a record of one otter that was chased for 28 miles (45 kilometres).

These creatures are well equipped for swimming. The strong tail functions as an excellent rudder and enables the animal to glide into the water without making a big splash. An otter may swim with all four legs drawn up against its body. When that is the case, the tail provides propulsion. Or, the otter may swim by rapidly moving its large, webbed hind feet.