Size:
Up to 60 pounds
25–35″ long, excluding the 1 ft. tail

Signs of their presence:

Flooded streams and beaver ponds; channels (tend to use the same routes).

Dams and dome-shaped lodges of sticks (usually aspen, willow, birch, and maple) caulked with mud. (Beavers will also build burrows in river banks, especially if living in a faster-moving stream or larger river)

Chewed branches and trees, piles of wood chips, fallen trees, and stumps, usually found very close to water. Teeth marks are obvious.

Sounds: Tail slap: their alarm call. Young whine, squeal, and moan at night, but it’s very hard to hear them.

Tracks: not often seen; back foot may be nearly as large as human hand; webbed toes.

Scats: look like saw dusty, ping-pong balls, usually left in the water at the bottom of a dam or lodge.

Distinctive, powerful scents.

“Mud pie” scent mounds: mud heaps perfumed with the beaver’s oily scent (castor) which mark the family’s territory. These heaps may be up to one foot tall and three feet wide, and are found at the water’s edge, or along river or pond banks

Common nuisance situations:

Time of year: Any time of year. From ice-out through June, new problems are often associated with the dispersal of the two-year-olds. From October through ice-up, beavers are preparing for winter by cutting many trees and working on their dams.

Plug culverts, drainage ditches, and drainpipes, which floods or washes out roads or driveways.

Beaver dams force water to collect against roads. This may saturate the road, causing potholes, settling, and instability.

Their dams may flood upstream areas. Flooding may damage roads or homes or kill crops and trees. It may make certain areas unusable.

Beavers cut down or girdle trees and shrubs for food. They can fell a tree that’s up to 2–3 ft. in diameter.

Beaver dams transform the environment. This will be good for some species and bad for others. Whether you see this as a problem or a gift depends on your perspective.

They may contaminate water supplies or interfere with sewer systems.

Disease risks: Rabies, tularemia, and Giardiasis (an intestinal infection caused by the protozoan, Giardia lamblia. There’s still much to learn about this parasite and how the disease is transmitted).
For more information:
http://nwco.net/09-appendixcbeyondtheroutine/9-06-Beaver.asp