The term FURRY RIVER MAMMAL is an otter, which is a five-letter mammal that lives in rivers and has a thick coat of fur. Otters are semi-aquatic mammals that live in both fresh and salt water habitats. They are members of the Mustelidae family, which includes weasels, badgers, and wolverines. Otters have webbed feet and a long, streamlined body that helps them swim quickly. They are also known for their playful behavior and intelligence.