River Otters can be thought of - and in a very real sense are - semi-aquatic weasels. Like fishers, martens, and mink, they have long, slender bodies, short limbs, and a short face, plus a set of adaptations for their aquatic lifestyle: an oily, waterproof coat, webbed toes, and small external ears. Learn more about the Lontra canadensis (Lutra canadensis), more commonly known as a Northern River Otter, in this easy-to-read species overview by the Smithsonian's National Museum of Natural History.