Once found throughout thousands of kilometers of Amazon waters, populations of river otters have been reduced to only two species, found mainly in remote headwaters and oxbow lakes. The larger species, the giant otter, is most commonly seen in lakes in Parque Nacional Manu, Reserva Nacional Tambopata in remotes areas of the Reserva Nacional Pacaya Samiria.

A family generally consists of a pair of adults plus a few juveniles. Their home is a mud cave in a lake bank marked by trampled vegetation and carefully placed boundaries of feces and urine.

The giant otter has stubby feet, which makes it an awkward land traveler, but a powerful flat tail, which makes it an impressively fast and acrobatic swimmer. With luck, otters can be seen and heard chomping on their fish catch from their log perches or even taking sun baths. Otters hunt baby caimans, snakes, and young turtles.

Though extremely inquisitive animals, they steer clear of predators such as adult black caimans and anaconda. If attached, however, a group of otters can use their powerful jaws and swimming abilities to prevail over these much larger predators.

Because of intense hunting between the 1940s and 1970s, otter populations have plummeted and become declared an endangered species. Even though it is illegal to hunt otters and sell their pelts, river otter populations continue to decline in some areas. Because they are at the top of the food chain, many biologists consider their decline to be a worrisome sign of watershed contamination from the mercury used in gold mining.