One of the key differences that distinguishes sea otters from river otters is their size.
Adult river otters tend to be smaller and more slender, with males reaching about 30 pounds (13.6 kilograms). They have four webbed feet adapted for both swimming and walking on land.
They have long tails that help them steer through rivers and lakes, and they’re known for their playful behavior, often sliding down muddy banks for fun.
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Sea otters, in contrast, can weigh up to 100 pounds (45.3 kilograms), making them much bulkier. Sea otters have the densest fur of any animal on Earth — up to a million hairs per square inch. Their thick fur keeps them warm in cold waters, eliminating the need for a blubber layer like other marine mammals.
These otters rely primarily on their hind limbs for swimming. Unlike the paws of river otters, sea otter hind feet have evolved into broad, flattened flipper-like structures which provide a large surface area for pushing against the water.
