Otters are very fastidious when it comes to cleanliness. This is due to the fact that, unlike many other marine mammals, otters do not have a layer of insulating blubber. They stay warm due to their dense, thick fur. If their fur becomes oiled or dirty, it can lose its warmth, and the otter can become very cold. Therefore, cleanliness is next to otter-ness!
(YouTube: Earth Unplugged)