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Sea Otter Vs River Otter (9 Key Differences)

When comparing the sea otter vs river otter, you may wonder if they the same animal. They are both weasel family members, as evident by their long, slender bodies. They may look similar, but they are two different creatures. From behavior and habitat to offspring and appearance, this article will detail the differences between these two otters.

Sea Otter vs River Otter: 9 Differences

Here’s a list of 9 ways that sea otters and river otters are different from one another.

1. River otters and sea otters are different species

Taxonomically speaking, river otters and sea otters are different genera. While both animals are classified as otters, river otters are members of the Lontra genus, and sea otters are members of the Enhydra genus. There are twelve different sub-species of river otter, but only three separate sub-species of the sea otter.

2. Sea otters are larger

Many people may not know this, but sea otters are much larger than river otters. The largest sea otters can weigh up to one hundred pounds, but river otters are much smaller.

The largest river otters weigh in at around thirty pounds. That’s quite the size difference!

3. Different fur

Sea Otter on the rock
Sea Otter on the rock | image by Jodie Wilson via Flickr | CC BY 2.0

You might not be able to tell by looking at them, but river otters and sea otters have very different fur. River otters actually have two layers of short, coarse fur. This inner layer keeps them warm, and the outer layer keeps them waterproof.

In contrast, sea otters actually have one layer of fur, which happens to be the densest fur of any other known animal. This results in river otters having short, sleek fur, while sea otters have long, fuzzy fur.

4. They live in different waters

River Otter in freshwater
River Otter in freshwater | image by caroline legg via Flickr | CC BY 2.0

River otters, despite their name, can be found in fresh and salt water. River otters also can often be found on the banks of the river. However, sea otters are only found in salt water and very rarely make their way onto land.

5. Number of offspring

river otter family in freshwater
River Otter family in freshwater | image by David Brossard via Flickr | CC BY-SA 2.0

Another significant difference is the number of offspring these creatures have. A river otter mother usually has between two and three babies, called pups. River otter mothers care for their pups until they are between six and twelve months old.

Conversely, sea otters only give birth to one pup and care for them until they are between eight and twelve months old. Another motherly difference is how these two creatures care for their young. River otters build dens on the riverbanks and care for their young there.

Sea otters carry their young on their stomachs to keep them safe until they are ready to swim by themselves. If they can’t keep them on their stomachs for some reason like if they are hunting, scientists have witnessed sea otters wrapping their young in kelp to keep them afloat while the mothers seek food.

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6. Sea otters are bigger

Sea Otter floats in the ocean
Sea Otter floats in the ocean | image by Mike’s Birds via Flickr | CC BY-SA 2.0

In addition to the difference in fur, river otters and sea otters have other differences in appearance. Sea otters are bigger and thus have larger feet than river otters. The sea otter does, however, have a shorter tail than the river otter.

7. Slightly different lifespans

River otters and sea otters have different lifespans. The average lifespan of a sea otter is twelve to fifteen years in the wild, but the average lifespan of a river otter is only nine to twelve years.

Scientists believe this difference is due to the size difference between the two creatures. Since river otters are much smaller, they are more prone to predators.

8. Different diets

River Otter eats fresh fish
River Otter eats fresh fish | image by Richard Griffin via Flickr | CC BY-SA 2.0

This is primarily due to the difference in habitat, but sea otters and river otters have different diets. River otters tend to eat frogs, fish, crayfish, reptiles, and birds.

Sea otters eat sea urchins, seaweed, clams, and crabs. Their diets are reminiscent of their environments.

9. Mating habits are different

River Otter mating
River Otter mating | image by _Veit_ via Flickr | CC BY-ND 2.0

Another major difference between sea otters and river otters is their mating habits. Did you know that sea otters mate for life? Well, they do.

Conversely, river otters mate with multiple partners during the course of their lives. In addition, sea otters tend to live in small to large familial groups, but river otters, especially males, are more territorial, and while they will be social, they prefer solitary lives or in small family groups.

What is a Sea Otter?

Sea Otter floats on the sea
Sea Otter floats on the sea | image by Dave Bezaire via Flickr | CC BY-SA 2.0

As their name suggests, sea otters are adorable mammals that barely leave their saltwater homes. They are one of the only mammals that use tools to help them hunt and feed, and they happen to have the densest fur of any other mammal on the planet.

They are unique sea creatures because they are the only marine mammals that can flip over rocks and boulders on the sea floor to find food. An adorable detail about sea otters is the fact that they hold paws when sleeping to avoid drifting away from their familial units.

What is a River Otter?

River Otter in wetland
River otter in wetland | image by marneejill via Flickr | CC BY-SA 2.0

These carnivorous mammals inhabit fresh and saltwater rivers. They are mostly solitary but come together in groups to mate.

These aquatic mammals split their time between the land and the water. River otters have a thick, lustrous coat that keeps them warm. When they are not in the water, river otters forage the land for food and build burrows or dens for their young.


You might think an otter is an otter, but hopefully, this article showed you that while two creatures can be called otters, they are very different. Not only do these two creatures have different habitats, but they have both evolved fur to best suit those habitats.

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In addition to the sea otter being significantly bigger than the river otter, they also have different mating and parenting habits. These two similarly named and look-alike animals are, in fact, very different. Do you think you can tell the difference if you saw them side-by-side?