9 Amazing Facts About River Otters

A pair of river otters resting on a log at the shoreline

BrianLasenby / Getty Images

North American river otters are semi-aquatic mammals endemic to the U.S. and Canada. Three other species: southern river otters, neotropical river otters, and marine otters are found in Central and South America and Mexico. North American river otters are classified as least concern by IUCN, while southern and marine river otters are endangered and neotropical river otters are near threatened.

River otters make their homes near lakes, rivers, swamps, and estuaries. They are adaptable thanks to long, thin bodies, thick fur, and webbed feet. An indicator species, they provide information about the health of their habitat. From amazing diving skills to bone-crushing teeth, discover the most interesting facts about North American river otters.

1. River Otters Are Not Sea Otters

North American river otters are not to be mistaken for sea otters, which live exclusively in the ocean. River otters, which weigh 20 to 25 pounds on average, are much smaller than sea otters, which weigh between 50 and 100 pounds. River otters spend part of their time on land and live in dens, while sea otters rarely come on shore. You can also tell a river otter by its long, sleek body, webbed and clawed feet, and long, muscular tail that is slightly flattened and tapers toward the end.

2. They Are Strong Swimmers

river otter swimming in blue water
imageBROKER/Jurgen & Christine Sohns / Getty Images

River otters are amazing swimmers. They can stay underwater for almost eight minutes and swim at a rate of nearly seven miles per hour. In a single dive, a river otter can travel as deep as 60 feet.

The eyes and ears of river otters are well-placed high on their heads for surface swimming. River otters swim on their bellies, and both their ears and nostrils can be closed for underwater swimming and diving.

3. They Can Also Walk on Land 

river otter walking on a log
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Though brilliant swimmers, river otters are as comfortable on land as they are in the water. River otters can walk and run easily on land, traveling as fast as 15 miles per hour. They are even agile maneuvering through vegetation, and are known to slide on slippery surfaces, like ice and mud, as a speedy way of getting from one place to another. 

River otters typically inhabit a range area of three to 15 square miles, but may travel as far as 10 to 18 miles a day to search for their favorite aquatic foods.

4. River Otters Are Social Creatures

group of river otters on a rock
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River otters are playful, social animals. Depending on their location, river otters may live alone, in pairs, or in small groups. Females live with their pups, and in some areas, males live in groups with other males. They often engage in group social behaviors like playing in the snow and wrestling each other in the water. This behavior not only creates bonds among the animals, it also allows young otters to learn and practice skills needed for hunting and survival.

Vocal animals, they communicate with sounds that include chirps, chuckles, whistles, and screams. River otters also leave scent markings in their area to convey information to their group. 

5. They Build Cozy Dens

River otters build their dens strategically. Dens are located close to the water line of rivers and lakes, and have multiple entrances underwater and on dry land. They are often excavated under trees or rocks, or in burrows abandoned by beavers or muskrats. River otters line their dens with leaves, moss, and grass. 

Females maintain the den and give birth to an average of two to three pups every year. Young pups are born helpless, and remain in the den until they are weaned at about three months.

6. River Otters Are Both Predator and Prey

Fast, agile swimmers with a mean bite, river otters have few natural predators when they are in the water. On land, however, they must be wary of predators such as bobcats, coyotes, mountain lions, wolves, black bears, and alligators. Even domestic dogs pose a threat to the river otter on land.

River otters use their long vibrissae, or whiskers, to locate prey in murky water. Carnivores, they feed primarily on aquatic creatures including fish, turtles, and crabs, and occasionally prey on birds and their eggs and small mammals.

7. They Have Bone-Crushing Teeth

River otters are equipped with 36 large, impressive teeth. Once they catch their prey, river otters use their powerful jaws and sharp teeth to make short work of their meal, even crustaceans. They have canines that deliver a lethal bite, and molars that are adapted for grinding and crushing prey, including those with shells, like mollusks.

They may consume smaller fish and prey at the water’s surface, but will bring larger fish to shore to eat.

8. They Are an Indicator Species

River otters play an important ecological role in their habitat. As apex predators that eat at the top of the food web, when pollutants enter their watershed habitat, river otters are the first to show signs of the existence of contaminants.

In addition, a strong and active river otter population is an indicator of a healthy habitat for otters, humans, and other species.

9. Some River Otters Are at Risk

While North American river otters have a stable population and are not considered at risk, the biggest threat to all river otters is humans. Southern river otters and marine otters are endangered, and neotropical river otters are near threatened. River otters have been hunted for their pelts since the 1500s, and in some areas they are still trapped for their fur.

By the late 1800s and early 1900s, river otters had disappeared from much of their historic range. Conservation projects to bring river otters back to their natural habitats have proven to be successful. However, oil spills, water pollution, ecosystem stresses, and habitat destruction continue to be threats to this semi-aquatic mammal. They are also accidentally caught in fishing nets and in traps set for beavers and raccoons.

Save the River Otters

  • Vote for and support environmental legislation that protects the environment.
  • Support the River Otter Ecology Project by making a donation or adopting an otter.
  • Donate to the Otter Specialist Group to support otter conservation and research programs.