River otters are incredibly well-adapted swimmers and divers, allowing them to pursue their preferred prey of fish. They can swim up to 7.5 miles per hour, dive as deep as 65 feet, and hold their breath underwater for 4-8 minutes. They also have specialized ears and nostrils that they can close to keep water out while they’re submerged, as well as webbed toes and a streamlined body to propel themselves through the water. Additionally, they have long, thick whiskers which allow them to sense prey even in dark, murky water. While many aquatic mammals such as whales or seals have blubber to keep them warm, river otters are dependent on their waterproof coats to keep them comfortable even in icy water. Their fur is incredibly dense, with up to 373,000 hairs per square inch! For comparison, humans have around 1,250 hairs per square inch on their heads! Otters spend lots of time maintaining their coats by grooming themselves and by rolling in sand, snow, or grass to help dry and fluff out their fur. Because of their incredible coats, river otters were a staple of the fur trade in the 1700’s and 1800’s, causing their populations to decline dramatically. Although they are now protected in many areas, river otters are still impacted by habitat loss and pollution of waterways.

River otters are often solitary, but in areas of high prey density, they have been known to hunt cooperatively and live in groups of up to 17 individuals, usually comprised of males. When food is scarce, however, only mothers and their offspring will coexist peacefully. River otters have a reputation for being incredibly playful, although this may be somewhat exaggerated; most examples of play are found in young otters or otters living in human care.