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The river otter is the longest of our weasels, ranging from 3 to 4 1/2 feet, of which the powerful, cylindrical tail (which thickens toward the base) comprises about one-third. Webbed toes and water-resistant fur suit the animal to a life spent largely in water. Otters sometimes paddle, but the force for swimming comes mostly from eel-like movements of the body and tail.

Otters are rich brown in color, with silvery brown beneath. The otter is about twice as long and five times as heavy as mink, and is the only other aquatic carnivore in the Rockies.

Once otters probably occurred in major streams statewide in Colorado, although they apparently have never been abundant. With settlement, subsequent water pollution and control of streamflows, otters disappeared from the state by the early part of this century. In the 1970s, however, the Colorado Parks and Wildlife began to restore populations to several drainages, including the Upper Colorado, the Dolores and the upper South Platte rivers. Otters live in riparian habitat, where aquatic animals like crayfish, frogs, fish, young muskrats and beavers are favored foods. Otters usually live in bank dens abandoned by beavers. They are active mostly at dawn and dusk, and appear to spend large amounts of time just playing—sliding on ice, snow and mud, and swimming gracefully for no apparent reason beyond swimming.

Otters breed in spring. Embryo implantation is delayed until the following winter, and one to four young are born in early spring. While the female is nursing one litter, mating occurs again.

The river otter's status in Colorado was recently changed from endangered to threatened. Find out more about this change and what it means for Colorado's river otters by watching our otter video (you can also see the text version ).

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Several Colorado mammals, including mink, beaver and muskrats, share the same habitat as river otters and are commonly confused with otters. All have dark brown fur and can be particularly difficult to distinguish from each other when they are swimming on the surface, partially submerged, especially when viewed from a distance. When viewed on land, however, their body shape, weight, size and tails are all quite distinctive.

If you are sure you have seen a river otter, please fill out our river otter observation form.

If you're not sure, read more below about other aquatic mammals that otters are commonly confused with.

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Mink:  Mink are semi-aquatic members of the weasel family like their larger cousin the river otter. Mink also have long bodies with short legs and small ears, but their bodies are slim and they have a triangular, flat skull. They also have dark brown fur, but have white spots on their chin and chest. Mink weigh between 1½ and 3½ lbs., only 10% the weight of otters. They are also smaller than otters, at about 1 to 2 feet in length from their nose to the tip of their furry, slender tail, which is less than one half the length of their body. Mink can be mistaken for young river otters; however otter pups would normally be accompanied by their mother, who would weigh around 15 lbs.

Beavers:  Beavers are North America’s largest rodent and are quite abundant in Colorado. They have large, stocky, rotund bodies with short legs, small eyes and ears, and prominent front teeth.  They have dark brown to almost black fur, with a paler underbelly. Beavers are heavier than otters, weighing between 30 and 60 lbs. Their head and body are about 3 feet long, and their flat, scaly, paddle-like tail ranges from 9” to 12” in length, differing significantly in shape from the otter’s long, tapered tail.

Muskrats:  The muskrat is a semi-aquatic rodent, like their much larger cousin the beaver. They have a similar body shape to the beaver, with a stocky, rotund body, short legs, and small eyes and ears. They also have dark brown fur.  Muskrats weigh between 2 and 4 lbs., only about 13% the weight of otters. They are about 26” in length from their nose to the tip of their long, narrow tail, which is about 8” to 10” in length. Their tail is black, scaly, and resembles that of a rat, but is flattened side-to-side, differing markedly in shape from the otter’s tail.