River mammals are aquatic animals that live in rivers and other freshwater habitats. The most common river mammal is the otter, which has a streamlined body and webbed feet for swimming. Otters come in many different species, including the five-letter Eurasian otter and the six-letter North American river otter. Another unique river mammal is the PLATYPUS, an eight-letter egg-laying mammal with a duck-like bill and webbed feet. It is found in rivers and streams in eastern Australia.