Beavers are aquatic mammals, they live in/near water, and are excellent swimmers. Their back feet are webbed like ducks, and they use their large, flat tails as rudders, for balance to stand up, or to slap the water in warning. When swimming usually only their head is out of the water. Underwater they have inner transparent eyelids, and both the ears and nose have flaps that close - they can stay underwater up to 15 minutes.
Beavers do not hibernate, and are active all winter - they store a stash of branches underwater in the fall to have food for winter. Their very thick fir keeps them warm, but it is not waterproof - they have to groom it constantly with oil from their castor glands.
Beavers are safe in water, but their short legs make them slow and vulnerable on land, so they need to build dams and ponds for protection from predators and to be close to food sources. The water needs to be deep enough to protect the underwater entries to their lodges, and deep enough not to freeze solid in winter, so they have access to their food.
About Beavers - the North American Beaver (castor canadensis)
Beavers are North America's largest rodent, larger than most people would think. Adults can be 40-60+ pounds. You may not have seen these shy and mostly nocturnal animals. Beavers form strong family units - the adults mate for life. Both parents care for one or more kits (babies) born in the spring. Kits stay with the family for 2-3 years, to help and play with younger kits and to learn the important beaver skills they need to survive. At 2-3 years old beavers go off to find their own territory, even across land, a dangerous time for young ones.
Beavers are herbivores - strictly vegetarian - They do NOT eat fish! They eat the leaves, roots, twigs and inner bark of aspen, willow and other fast growing trees and plants. They also comsume algae and other plants that can clog streams. Beavers have pairs of upper and lower incisors, which are always growing, so they always need to be chewing. Their teeth get orange from iron in the food they eat - their teeth are whiter when they are younger.
This keeps all other beavers away, so there are never too many beavers on any creek.
Populations are also limited by available food.
The beaver below is marking his territory by making a scent mound.
Beavers are very territorial, and define their territory with scent mounds made of mud, and marked with scent from their castor glands. This lets other beavers know that
"this spot is taken".