These long, slender creatures are well-equipped for their aquatic habits. They have membranes between the fingers for better swimming, and their bones show osteosclerosis, increasing their density to reduce buoyancy in the water.
These animals may inhabit any unpolluted body of fresh water, including lakes, streams, rivers, and ponds, as long as the food supply is adequate. European otters may also live along the coast, in salt water, but require regular access to fresh water to clean their fur. They feed mainly on fish and shellfish, living over 10 years in clearly marked territories.