This South American otter is the world's largest, at some 6 feet (1.8 meters) long. It lives only in the rivers and creeks of the Amazon, Orinoco, and La Plata river systems.
These huge members of the weasel family swim by propelling themselves with their powerful tails and flexing their long bodies. They also have webbed feet, water-repellent fur to keep them dry and warm, and nostrils and ears that close in the water.
Fish make up most of the giant river otter's diet. They hunt alone or in groups, sometimes using coordinated efforts, and must be successful often to meet their daily intake quota. Each animal may eat six to nine pounds (three to four kilograms) of food per day. Fish are supplemented by crustaceans, snakes, and other river creatures.
Giant river otters live in family groups which include monogamous parents and the offspring from several breeding seasons. They den by burrowing into banks or under fallen logs, and establish a home territory that they will aggressively defend.
Like most other otter species, giant river otters come ashore to give birth. Females retreat to their underground dens and deliver litters of one to six young. Young otters remain in the den for a month but grow up quickly. After nine or ten months, it is difficult to tell mother from child.
Giant river otters have been hunted extensively and are now among the rarest otters in the world—only a few thousand are believed to survive in the wild.