The North American River Otter is problably the most numerous otter species. They exhibit delayed implantation with breeding in March-April and birth in late winter/early spring. Fossils of North American River Otters have dated back to the Pleistocene period and archeological remains have been uncovered from 200 B.C. to the mid-1400s.

North American River Otters once lived throughout North America. Native Americans hunted otters largely for their dense fur which allowed them to keep warm. When European settlers arrived and started developing the land (cutting down forests) and using farm pesticides and fertilizers, the otter habitat became threatening. By the early 1980s, eleven states reported no otter population and thirteen other states reported scarce numbers. As a result, numerous reintroduction programs were established to repopulate many of these areas. By late 1990s, many of these programs had successes with a dramatic improvement in returning otters to their original range.

Size
From a medium size to a large size. The head and body are 660 to 1070mm long. The tail is 315 to 460mm long. The total length then is 1000 to 1530mm.

Feet
The North American River Otter's feet are strong and well webbed. Their claws, which are very strong, also add to the strength.

Hair
The hair, like most Otters, is velvety and thick. Their guardhairs are thick, 17 to 20mm long. Their underfur is 8 to 9mm long.

Color
On the North American River Otter's back, it is very dark, nearly black to reddish or sometimes grayish brown. On it's belly it is lighter, silvery or grayish brown. The throat and cheeks are silvery to yellowish gray, but not clearly distinguished from upper parts.

Nose
The nose is diamond shaped, with two nostrils at the lower half. The nostrils go about 1/4 of the way in to the center of the nose.