The otter is a playful, semiaquatic mammal belonging to the weasel family Mustelidae . They have slender bodies, short legs, strong necks, and long, flat tails that aid in swimming. Most species have webbed feet, which enhances their swimming abilities. Otters can be found in various shades of brown with lighter underparts. There are 13 species of otters, two of which are marine species, while the others live mainly in fresh water. They range in size from the Asian small-clawed otter, weighing 3 kg (6.6 pounds), to the giant otter, weighing 26 kg (57 pounds), and the sea otter, weighing 45 kg (99 pounds). River otters eat fish, crayfish, crabs, mussels, and frogs.

Where do otters live?

Otters can be found in a variety of habitats across the globe. River otters inhabit freshwater ecosystems such as rivers, lakes, and wetlands in North and South America, Europe, Africa, and Asia. They eat fish, crayfish, crabs, mussels, and frogs. Sea otters are exclusively marine and live in the coastal waters of the northern Pacific Ocean, from the Kuril Islands to California. They feed on sea urchins, crabs, and shellfish, often using rocks to crack open their prey. The marine otter, a relative of the sea otter, lives along the rocky Pacific coast of South America.

Otters' diets vary depending on their species and habitat. River otters are opportunistic eaters, consuming available prey like fish, crayfish, crabs, mussels, and frogs. They hunt visually in shallow water, using their dexterity and vibrissae (sensory hairs) to find prey under rocks. Sea otters, found exclusively in marine environments, eat sea urchins, crabs, and shellfish, often using rocks to crack open their prey. Marine otters, a smaller South American species, feed on crustaceans, mollusks, and fish, but unlike sea otters, they do not eat many sea urchins.

How do otters adapt to living in water?

Otters, members of the weasel family, have several adaptations for their semiaquatic life. Most otter species have webbed feet that enhance their swimming ability. River otters use sensory hairs called vibrissae on their snouts to detect water turbulence, helping them find prey in murky water. Additionally, otters that move between air and water have uniquely shaped corneas that allow them to see effectively both in and out of the water. Their slender bodies, short legs, strong necks, and long, flattened tails also aid in graceful movement through the water.

What kinds of social behaviors do otters have?

Otters exhibit a range of social behaviors. River otters can spend time on land, foraging for food such as fish and frogs, while sea otters stay in marine environments, consuming sea urchins, crabs, and shellfish. Sea otters use rocks to crack open their prey and will float on their backs, sometimes holding each other's paws to create "rafts" while sleeping to avoid drifting away. River otters reach sexual maturity faster and have multiple pups per litter, while sea otters mature slowly and usually have one pup at a time. Sea otter mothers place pups on their stomachs while swimming or wrap them in kelp while hunting, whereas river otters keep pups close or in burrows. Aggressive behavior in animals, including otters, usually occurs due to competition for food and mates.

How are otters important to their ecosystems?

Otters play a crucial role in their ecosystems. As predators, they help maintain balance in aquatic environments by controlling populations of prey species like fish, crabs, and sea urchins. Sea otters are known to consume sea urchins, which allows kelp forests to flourish, in turn benefiting the fish and other species that rely on kelp forests. River otters are opportunistic hunters, preying on whatever is most readily available, and helping to maintain the balance of the food web in their environments. However, otter populations face increasing threats from habitat destruction, pollution, and human activities. Conservation efforts, such as protecting wetlands and restoring water quality, are essential for ensuring the future of these important mammals and the ecosystems they inhabit.

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References & Edit History Quick Facts & Related Topics

Images, Videos & Interactives

Witness the playful gliding and fishing of river otters in a freshly thawed North American river

Spotting wild otters in the Shetland Islands

At a Glance

otter summary

otter

mammal

Also known as: Lutrinae

Written by

Serge Lariviere

Fact-checked by

Britannica Editors

Last updated

Oct. 28, 2026 •History

Top Questions

What is an otter?
The otter is a playful, semiaquatic mammal belonging to the weasel family Mustelidae. They have slender bodies, short legs, strong necks, and long, flat tails that aid in swimming. Most species have webbed feet, which enhances their swimming abilities. Otters can be found in various shades of brown with lighter underparts.

There are 13 species of otters, two of which are marine species, while the others live mainly in fresh water. They range in size from the Asian small-clawed otter, weighing 3 kg (6.6 pounds), to the giant otter, weighing 26 kg (57 pounds), and the sea otter, weighing 45 kg (99 pounds). River otters eat fish, crayfish, crabs, mussels, and frogs.
2 Britannica Sources
1. Gorilla gorilla, Sula sula, and Other Animals Whose Names Are Tautonyms—the Same for Genus and Species: Eurasian otter (Lutra lutra)
2. otter
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Where do otters live?
Otters can be found in a variety of habitats across the globe. River otters inhabit freshwater ecosystems such as rivers, lakes, and wetlands in North and South America, Europe, Africa, and Asia. They eat fish, crayfish, crabs, mussels, and frogs. Sea otters are exclusively marine and live in the coastal waters of the northern Pacific Ocean, from the Kuril Islands to California. They feed on sea urchins, crabs, and shellfish, often using rocks to crack open their prey. The marine otter, a relative of the sea otter, lives along the rocky Pacific coast of South America.
4 Britannica Sources
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What do otters eat?
Otters' diets vary depending on their species and habitat. River otters are opportunistic eaters, consuming available prey like fish, crayfish, crabs, mussels, and frogs. They hunt visually in shallow water, using their dexterity and vibrissae (sensory hairs) to find prey under rocks. Sea otters, found exclusively in marine environments, eat sea urchins, crabs, and shellfish, often using rocks to crack open their prey. Marine otters, a smaller South American species, feed on crustaceans, mollusks, and fish, but unlike sea otters, they do not eat many sea urchins.
2 Britannica Sources
1. otter: Freshwater otters
2. What’s the difference between river otters and sea otters?: Behavioral differences
Created from Britannica articles using AI. AI can make mistakes, so verify using Britannica articles.
How do otters adapt to living in water?
Otters, members of the weasel family, have several adaptations for their semiaquatic life. Most otter species have webbed feet that enhance their swimming ability. River otters use sensory hairs called vibrissae on their snouts to detect water turbulence, helping them find prey in murky water.

Additionally, otters that move between air and water have uniquely shaped corneas that allow them to see effectively both in and out of the water. Their slender bodies, short legs, strong necks, and long, flattened tails also aid in graceful movement through the water.
6 Britannica Sources
Created from Britannica articles using AI. AI can make mistakes, so verify using Britannica articles.
What kinds of social behaviors do otters have?
Otters exhibit a range of social behaviors. River otters can spend time on land, foraging for food such as fish and frogs, while sea otters stay in marine environments, consuming sea urchins, crabs, and shellfish. Sea otters use rocks to crack open their prey and will float on their backs, sometimes holding each other's paws to create "rafts" while sleeping to avoid drifting away. River otters reach sexual maturity faster and have multiple pups per litter, while sea otters mature slowly and usually have one pup at a time. Sea otter mothers place pups on their stomachs while swimming or wrap them in kelp while hunting, whereas river otters keep pups close or in burrows.

Aggressive behavior in animals, including otters, usually occurs due to competition for food and mates.
3 Britannica Sources
Created from Britannica articles using AI. AI can make mistakes, so verify using Britannica articles.
How are otters important to their ecosystems?
Otters play a crucial role in their ecosystems. As predators, they help maintain balance in aquatic environments by controlling populations of prey species like fish, crabs, and sea urchins. Sea otters are known to consume sea urchins, which allows kelp forests to flourish, in turn benefiting the fish and other species that rely on kelp forests. River otters are opportunistic hunters, preying on whatever is most readily available, and helping to maintain the balance of the food web in their environments.

However, otter populations face increasing threats from habitat destruction, pollution, and human activities. Conservation efforts, such as protecting wetlands and restoring water quality, are essential for ensuring the future of these important mammals and the ecosystems they inhabit.
3 Britannica Sources
Created from Britannica articles using AI. AI can make mistakes, so verify using Britannica articles.

otter, (subfamily Lutrinae), any of 13 species of semiaquatic mammals that belong to the weasel family (Mustelidae) and are noted for their playful behavior. The otter has a lithe and slender body with short legs, a strong neck, and a long flattened tail that helps propel the animal gracefully through water. Swimming ability is further enhanced in most species by four webbed feet. Two species are marine, and the others living predominantly in fresh water. Otters range in size from 3 kg (6.6 pounds) in the Asian small-clawed otter (Aonyx cinereus, formerly Amblonyx cinereus) to 26 kg (57 pounds) in the giant otter (Pteronura brasiliensis) and 45 kg (99 pounds) in the sea otter (Enhydra lutris). Fur colour is various shades of brown with lighter underparts.

Freshwater otters

The 11 species often referred to as river otters are found throughout North America, South America, Europe, Africa, and Asia in freshwater ecosystems that sustain an abundance of prey such as fish, crayfish, crabs, mussels, and frogs. Most river otters are opportunistic, feeding on whatever is most easily obtained. Diet often varies seasonally or locally, depending on which prey is available. River otters hunt visually while chasing fish, but they use their manual dexterity to dislodge crabs and crayfish from under rocks. Sensory hairs on the snout called vibrissae also assist by sensing water turbulence. After being captured in the teeth or forefeet, prey is consumed either in the water or on shore. River otters hunt more effectively in shallow water than in deep water, and, although they are proficient swimmers, all prefer slow-swimming species of fish. African clawless otters (Aonyx capensis) and Congo clawless otters (A. congicus or A. capensis congicus) occupy murky waterways and thus rely more on manual dexterity than on vision to obtain food (mostly crabs) from under rocks. Their front feet are handlike and partially webbed.

Most travel is aquatic, but river otters can venture swiftly overland between bodies of water. They typically follow the shortest route possible and often establish much-used trails. While in the water, they constantly search features such as logjams and deepwater pools for prey. To rest, otters seek refuge in underground holes, rock crevices, beaver lodges, cavities in root systems, or simply dense vegetation along the shoreline. When not resting or eating, river otters can often be seen eagerly sliding down mud or snow banks. Many species establish regular latrine sites along the shores of lakes or rivers. Such stations may facilitate communication between individuals.

Litter size ranges from one to five. Young otters (pups) may fall prey to large raptors, and various carnivores may kill adults traveling on land. In warmer regions crocodiles and alligators are threats. However, most mortality results from human activities, in the form of road kills, drownings in fishnets, destruction as pests around fishing areas, or trapping for their fur.

Saltwater otters

Sea ottersA pair of sea otters at the Vancouver Aquarium, Stanley Park, Vancouver, British Columbia, Canada.

Two otter species are strictly marine: the sea otter (Enhydra lutris) of the Pacific Coast of North America and the much smaller marine otter (Lontra felina) from the coast of Peru and Chile. Both rely exclusively on marine prey, although the sea otter can be found much farther offshore; the marine otter stays within about 100 meters (330 feet) of the shore.

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Sea otters are well adapted to marine life. The front and back feet are fully webbed; large lungs allow long dives and provide buoyancy; and thick fur provides insulation. Moreover, sea otters can drink salt water and thus can remain at sea for several days at a time. Sea otters are usually solitary but are sometimes seen in groups; gatherings of up to 2,000 have been observed along the coast of Alaska. At night, sea otters may choose either to sleep on land or simply to rest afloat near beds of kelp, and they often float in groups, grasping one another’s forefeet to create large rafts or pods, which may comprise as many as 1,000 individuals. Sea otters feed mainly on sea urchins and on crabs and other shellfish. Fish are also eaten. Captured prey is eaten at sea while the otter floats on its back. Rocks are typically used to break open crabs and other shellfish, whereas sea urchins are crushed with the forefeet and teeth. Sea otter predation on the herbivorous urchins (genus Strongylocentrotus) enables kelp forests and the fish associated with them to flourish. However, large numbers of sea otters can deplete shellfish populations, competing with fisheries for crabs, clams, and abalones. Female sea otters give birth in water to only one young at a time, and the young remains dependent on the mother until six to eight months of age. Sharks and killer whales eat sea otters on occasion.

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(Read Britannica’s essay “How Do Sea Otters Stay Warm?”)

The marine otter, or chungungo, is really a freshwater otter that has learned to occupy marine environments in South America. This small (3–6 kg [6.6–13.2 pounds]) otter occurs on the Pacific coast from Peru through Chile and Tierra del Fuego in Argentina. It is mostly solitary, and only rarely do groups of more than three animals occur. Marine otters occupy the intertidal zone that covers the first 100–150 meters (roughly 330–500 feet) of coastal water and about 30 meters (100 feet) inland. They feed on crustaceans such as crabs and shrimp, as well as mollusks and fish. Interestingly, marine otters do not consume sea urchins as extensively as do sea otters, even though sea urchins often are common where marine otters live. Unlike sea otters, marine otters shelter in rock cavities for daytime rest, breeding, giving birth, and raising young.

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Freshwater otters

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Saltwater otters