North American River Otter: Facts, Diet and Habitat

Appearance: built for water

A river otter has a long, streamlined body, short legs, a broad flat head with small ears and a thick, muscular tail that tapers to a point. The tail makes up about a third of its total length and acts as a rudder and a powerful paddle. All four feet are fully webbed and have claws.

The fur is dark brown to almost black on the back, lighter below, and often silvery or golden brown on the throat and cheeks. It has two layers: long, glossy guard hairs and a very dense underfur that traps air and keeps the skin dry. Otters spend a lot of time grooming to keep this coat waterproof.

Long, stiff whiskers (vibrissae) detect the movements of prey in dark or muddy water. The nostrils and small ears close when the otter dives, and a clear inner eyelid, the nictitating membrane, protects the eyes underwater. Their eyes are adapted for seeing underwater, which may make them a little nearsighted on land.

How big is a North American river otter?

Males are larger than females. An average male weighs about 11 kg (25 lb) and an average female about 8 kg (18 lb), and big males can top 15 kg (33 lb). The North American river otter is larger than the Eurasian otter on average but much smaller than the sea otter, which can weigh up to about 45 kg (99 lb).

Habitat and range

Despite its name, this otter lives in almost any permanent water with enough food and cover: rivers, streams, lakes, ponds, marshes, swamps, estuaries and rocky sea coasts. It tolerates cold winters and high mountains, and in the north it hunts under the ice through breathing holes and air pockets.

Its range covers most of Canada and Alaska, the Pacific Northwest, the Great Lakes region, New England, the Atlantic and Gulf coast states and much of the Midwest and Rocky Mountains. In Mexico it is limited to the Rio Grande and Colorado River deltas. It is rare or missing in the driest parts of the Southwest.

River otters do not dig their own dens. They use the old burrows of beavers, muskrats and woodchucks, hollow logs, rock piles, dense vegetation and the spaces inside beaver lodges. Many dens have an underwater entrance. See Where do otters live? for otter habitats around the world.

Diet: what do river otters eat?

River otters are carnivores, and fish are their main food almost everywhere. They mostly catch slow-moving fish such as suckers, carp, catfish, sunfish and perch, rather than fast game fish such as trout, which they take mainly when the fish are spawning or sluggish in cold water. An adult can eat about 1–1.5 kg (2.2–3.3 lb) of fish a day.

Crayfish are the second most important food and in some places, at some times of year, they are eaten more than fish. River otters also take crabs, frogs, salamanders, turtles, snakes, aquatic insects, molting ducks and other water birds, and occasionally small mammals. They avoid carrion.

Small prey is eaten in the water, while larger fish are carried to the bank. Otters usually hunt alone or in family groups, often at dawn, dusk and night, but they can be seen at any time. For more on otter meals, see What do otters eat?.

Swimming and diving

River otters swim by undulating the body and tail and paddling with their webbed hind feet. Most hunting dives are short, well under a minute, but they can stay submerged for up to about 8 minutes and are reported to dive to around 18 m (60 ft). Read more in How long can otters hold their breath?.

On land they are surprisingly quick, running at up to about 29 km/h (18 mph). They often travel several kilometers overland between waterways, and in winter they cross snow by alternating bounds with belly slides.

Behavior: play, scent and family life

North American river otters are known for play. They slide down mud banks and snow slopes, wrestle, chase each other and toss pebbles or sticks. Play helps young otters build hunting and fighting skills and strengthens bonds between group members.

Social life is flexible. Adults often live alone or in loose groups, while a mother and her pups form a family unit that stays together for many months. In some coastal areas, groups of males live and hunt together. Home ranges are large, from a few kilometers to around 78 km (48 mi) of waterway, depending on how rich the food supply is.

Otters communicate with whistles, chirps, chuckles, growls and screams. They also scent-mark using musky glands near the base of the tail and by leaving droppings, called scat or spraint, at regular latrine sites on rocks, logs and banks.

Reproduction and life cycle

River otters mate in late winter or spring. Thanks to delayed implantation, the fertilized egg rests for months before it attaches and starts developing, so the total time from mating to birth can approach a year, although true development takes only about two months. This trait sets the species apart from the Eurasian otter.

Pups are born from November to May, with a peak in March and April. A litter has one to six pups, usually two or three. They are born furred but blind and helpless, open their eyes at about one month and first swim at around two months, often coaxed into the water by their mother. They are weaned at about three months and usually stay with the family until the following spring. Otters reach maturity at two to three years.

In the wild, North American river otters usually live about 8–13 years. In captivity they can reach 21–25 years.

Predators and threats

Healthy adult otters have few natural enemies, but bobcats, coyotes, American alligators and large birds of prey occasionally take them, especially young otters. Their agility and fierce defense protect them from most attacks.

The biggest threats come from people. Unregulated trapping for fur, habitat loss and water pollution wiped otters out of large parts of the central and eastern United States by the early 20th century. Otters are very sensitive to pollution, including mercury and other chemicals that build up in fish, and to oil spills along coasts.

Conservation status and comeback

The IUCN Red List classifies the North American river otter as Least Concern. It is listed in Appendix II of CITES, which controls international trade in its pelts.

Its recovery is one of North America’s wildlife success stories. Starting in the 1970s, about 20 US states reintroduced otters, often using animals from Louisiana and other strongholds. Missouri, Kentucky, Colorado, Pennsylvania, West Virginia and New York are among the states where released otters have spread through river systems. Cleaner water and regulated trapping have helped, and otters have returned even to some cities.

River otter vs sea otter

The North American river otter is often confused with the sea otter, especially on the Pacific coast where both live. The sea otter is much heavier, rarely comes ashore, floats on its back to eat and has a short, flat tail. The river otter swims belly-down, regularly leaves the water to rest and groom, and has a long, thick tail.

See sea otter vs river otter for the full comparison.

River otters and people

For Indigenous peoples and later for European fur traders, the river otter was valued for its thick, hard-wearing pelt. Trapping remains legal and regulated in many US states and Canadian provinces, where wildlife agencies set seasons and limits to keep populations healthy.

Today many people know otters as a favorite at zoos and aquariums and as a sign of a clean river. Because otters sit near the top of the aquatic food chain and quickly disappear from polluted water, their return is often treated as good news for whole river systems.

Conflicts do occur. Otters sometimes raid fish farms and garden ponds, and on docks and boats along the coast their latrines can be smelly.

Watching wild otters is a rewarding experience. Quiet early mornings along lakeshores, marsh boardwalks and rocky coasts offer the best chances. Look for tracks with five webbed toes, slides in mud or snow, and latrine sites full of fish scales and crayfish shells. Keep a respectful distance, never feed otters, and keep dogs leashed, since a mother defending her pups can be fierce.