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The City of Portland, Oregon

Environmental Services

working for clean rivers

Phone: 503-823-7740

Fax: 503-823-6995

1120 SW 5th Ave, Suite 613, Portland, OR 97204

More Contact Info

Beaver, Muskrat and Nutria Identification

beaverThe American beaver is a native mammal that plays an important ecological role in our watersheds. It's also a species of management concern for some landowners. This page has information aobut how to tell the difference between beavers, muskrats and nutria.

American Beaver (Castor canadensis)


  • Broad (horizontally flattened) and almost hairless tail
  • Length is between 39 and 47 inches
  • They weigh between 35 and 50 pounds or more.
  • Fur color appears reddish brown to black
  • Each foot has five digits
  • The hind feet have webbing, but the front do not 

Also Look For

  • tree felled by beaversGirdled or felled trees, limbs with bark removed
  • Beaver prefer certain tree and shrub species including aspen, cottonwood, willow, conifers, fruit trees, and ornamentals
  • Dams and lodges made from limbs and mud
  • Primary dam-building time is August through October
  • Slides or slicked-down paths where they enter and leave water, 15 to 20 inches wide and at right angles to the shoreline
  • Channels that lead to their ponds (sometimes look human made) 

Muskrat (Ondatra zibethicus)


  • Much smaller than a beaver, but not as large as a nutria
  • muskrat swimmingAbout 16 to 25 inches long
  • May reach a maximum of four pounds
  • Long, rat-like tail that is flattened vertically
  • Dense, grayish under fur overlaid by long, glossy guard hairs that vary in color from dark brown to yellowish brown; guard hairs are long and coarse on the back and finer on the side and the belly 

Also Look For

  • muskrat lodgeLodges that are smaller than beaver lodges and built from marsh vegetation, not sticks
  • Food consists almost entirely of aquatic and semi aquatic vegetation including grasses, rushes, sedges, cattails, etc.

Nutria (Myocastor coypus)


  • nutriaMuch smaller than the beaver; much larger than the muskrat
  • May reach a maximum of 20 pounds
  • Mature adults are about two feet long
  • Muzzle is covered by white coarse hair
  • Tail is hairy and round (not compressed from side to side) and pointed at the tip
  • Hind legs are much longer than the front legs, giving them a hunched appearance when on land
  • Hind feet are webbed
  • Large incisors are yellow to orange-red

Also Look For

  • Floating platforms up to three feet high that they make from aquatic vegetation
  • Burrows in vegetated banks near waterways and collapsing banks and road beds

For More Information