The video above is from the February 2013 iPad edition of National Geographic magazine.

River otters are playful animals. But did you know these mammals are also top predators? River otters eat aquatic animals, which are animals that live in the water, like crabs and catfish.

Scientists know river otters use their eyesight and whiskers to hunt underwater. Their whiskers feel movement in the water—the swish of a fish's tail, for example. But could river otters rely on another sense? Charlie Hamilton James thinks so. He thinks otters can smell underwater.

Charlie lives near a river in western England. He’s been photographing river otters since he was 16 years old. Charlie wanted to see if an otter could find a dead trout in cloudy water at night. The otter wouldn’t be able to use its whiskers because the fish wouldn’t be moving. It wouldn’t be able to see the fish because the water was too murky.

Charlie set up night-vision cameras on the riverbank. He also put waterproof cameras in the river near the trout. He saw what was happening in the river from small screens set up in his kitchen. He was lucky. Two otters visited his section of the river. Watch the video to find out if they found the fish!