River Otters are long, muscular, and very streamlined animals, well adapted for their aquatic existence. The brown to brownish-gray fur is short and water repellent. The ears are small and lie flat against the side of the head. An otter’s feet are strongly webbed and the tail is long and rudder-like. A clear, third eyelid called a nictitating membrane, covers the otter’s eyes when swimming under-water. This gives protection to the eye but allows the otter to see clearly. A typical adult otter weighs between 11 and 23 pounds and can measure three to four feet in length.