A beaver's length is 3-4 feet, including their large flat tail. Their tail acts as a prop when they sit or stand, it acts as a rudder when they swim, and it acts as a warning sign to others (by slapping the water) when danger is near. Beavers can weigh as much as 60 pounds. The female is normally as large as or larger than the male, which is unusual for mammals. They have dark brown fur that is waterproof and webbed hind feet. Their eyesight is poor but other senses (hearing, smell and touch) are keen. Their eyelids are transparent and act as goggles when underwater.
Beavers have large front teeth that protrude from their mouth. They never stop growing so they must gnaw on wood often to keep them trimmed. Their ears and noses have valves that close when underwater. This prevents water from getting in their mouth when they chew on submerged wood. They are able to stay underwater for about 15 minutes at a time.