The Sea otter is one of the few sea MAMMALS. They are brown with a strong tail for swimming. They have extremely thick fur to keep warm. They weigh between 30 and 100 pounds, making them the heaviest member of the weasel family. They are between 3 and 7 feet long, including their tail. Their population today is 150,000–300,000. They were once hunted for their fur, but today they are endangered because of the destruction of their homes.