The North American River Otter, Lontra canadensis, also known as the Northern River Otter, is a North American member of the Mustelidae or weasel family. It is a common animal in North American waterways. Its numbers have significantly dropped since Europeans came to colonize the Americas.

The Northern American river otter is a species of otter. It is a member of the genus Lontra, which is comprised of New World otters. It was previously included, with the other members of Lontra, in the genus Lutra, but was placed in a newly-created genus when it was determined that the New World otters are more closely related to the genera Lutrogale and Pteronura than to the other species in Lutra.

The Northern Otter has a streamlined, muscular body with short legs, webbed toes and a long muscular tail. The North American river otter’s body measure is somewhere between 0.66m (26") to 1.07m (42"), and its tail measure is between 0.30m (12") to 0.46m (18"); a river otter’s tail makes up 30 to 40% of the total length of its body. It can weigh between 3 kg and 14 kg (6 and 31 pounds). The river otter has a round, small head, short yet powerful legs, and large whiskers. Otters display sexual dimorphism, as the male otter is often larger than the female. Its fur is glossy and dark brown, and the throat is often silver gray.

The Northern American river otter is found throughout North America, inhabiting inland waterways and coastal areas in Canada, Alaska, the Pacific Northwest, the Atlantic states, and the Gulf of Mexico.

Although commonly called a "river otter", the name can be misleading, as it inhabits marine as well as freshwater environments, and the freshwater environments include standing bodies of water such as lakes. Some populations permanently reside in marine shoreline habitats, and are often mistaken for sea otters. River otters can be distinguished from sea otters by the former's narrower faces and differences in behavior: Sea otters always eat floating on their backs in the water, whereas river otters bring their prey ashore to eat.

The North American river otter is found in a wide variety of aquatic habitats, both freshwater and coastal marine, including lakes, rivers, inland wetlands, coastal shorelines and marshes, and estuaries. It can tolerate a great range of temperature and elevations; its main requirements are a steady food supply and easy access to a body of water. However, the North American river otter is sensitive to pollution, and will disappear from polluted areas.

Like other otters, the North American river otter lives in a holt or den . The den is constructed in the burrows of other animals, or in natural hollows, such as under a log or in river banks. An underwater entrance or an above-ground entrance leads to a nest chamber which is lined with leaves, grass, moss, bark, and hair. It often uses dens built by other animals, sometimes killing beavers or muskrats to take over their lodges.

North American river otters are trapped for their highly-prized fur. Over-harvest in the 1800s has led to its disappearance from many parts of its historical range. Trapping is still permitted in some areas where otters remain abundant. In other areas, the otter is being restored to places where it may have long since been extirpated, such as the Hudson River. The North American river otter is not a nationally endangered species, but it is endangered in many states and it is listed as threatened by others. Over-hunting, habitat destruction, and inadequate laws protecting the North American river otter are major factors where otters remain threatened. Since the discovery of the Americas, hunters have captured and killed the otters for their pelts. Hunting still continues today, otter pelts being worth over $100 (USD) each. Over 30,000 otter pelts are sold each year in the United States and Canada. Efforts have been made to bring the otter back from endangerment. Since 1986, the National Park Service has reintroduced over 100 North American River Otters back into the wild.

The North American River Otter is a highly active predator, like its relatives, the weasels. It is very playful, chasing, sliding, swimming, jumping, and wrestling. This makes it popular for zoo exhibits. However, otters are not friendly towards humans if raised in captivity. Generally a captive-raised river otter (especially males) can begin to act defensive and becomes very aggressive towards humans when it reaches sexual maturity, and thus otters do not make good pets. There are times when otters have remained tame through their adult life. However, "tame" is a relative term; even the most human-friendly otter will still bite and scratch, sometimes quite badly. They can be highly curious animals and have been known to follow trout fisherman along the opposite bank.

Diet

The North American river otter is a carnivore. It mainly eats fish, but also insects, frogs, crustaceans and sometimes small mammals. On occasion some larger river otters will attack and kill water birds such as ducks, geese, and even herons. During their formative years, the fur on the underbelly of the otter acts as a filter as the otter swims, trapping small food items for later consumption. The North American river otter is capable of swimming in circles, which creates a whirlpool-like motion that brings fish from the bottom of the water up to the top. It is generally nocturnal or crepuscular, but is diurnal, active during the day, where undisturbed by human activity. It uses musk and urine to mark the land bordering their territories in a behavior called sprainting.

Reproduction

The reproduction of a river otter is a very complicated process. North American river otter exhibit delayed implantation. The fertilized egg does not implant in the uterine wall right away. Implantation is delayed for several months. The female is pregnant for almost a year. The actual gestation period is about 5-7 weeks until the pups are born.

Otters are only suited for professional exhibits or care. Their diet is flexible. Some groups feed their otters a variety of fresh water creatures in addition to live fish, while others live on a diet of processed meats. They need access to fresh water deep enough to swim and play in, and this water will need to be changed regularly or filtered. Some groups add chlorine to the water to reduce bacteria and algae growth, but this may result in skin problems for the otter. As they are very active, they are easy to train for medical exams, demonstrations, and behavioral enrichment. Common enrichment objects include ice with food frozen in it, floating balls, and segments of wide pipe.