Three semi-aquatic rodents distributed throughout the Pacific Northwest are the beaver (Castor canadensis), muskrat (Ondatra zibethicus), and nutria (Myocastor coypus). Each can easily be identified in hand, but it can be difficult to tell them apart in their aquatic habitats. All three species have lips that close behind their large incisor teeth. This allows the mouth to be sealed off while the large incisors protrude for underwater feeding.
