Otters are long and slim animals that can be longer than a meter. They have four short legs. They usually stay on all four legs, but they can stand up as well but they are expert swimmers and spend a lot of time in water. They have a thick fur coat that keeps them warm even in freezing water. They have very soft, insulated underfur, which is protected by an outer layer of long guard hairs. This traps a layer of air which keeps them dry and warm under water. They keep the air topped up by blowing into the fur with their mouth. Their fur is often brown at the top, and lighter underneath the Otter.