Giant Otter: Size, Facts & Where to See Them in Peru

The giant otter (Pteronura brasiliensis), called lobo de río in Peru, is the longest member of the weasel family: up to about 2 m (6.5 ft) from nose to tail and around 32 kg (70 lb), roughly as long as an adult person is tall. It lives in noisy family groups in the rivers and oxbow lakes of the South American lowland rainforest, and it is Endangered on the IUCN Red List. In Peru the best places to see it are Sandoval Lake in the Tambopata National Reserve and the Otorongo and Salvador oxbow lakes in Manu National Park.

Giant otter facts at a glance

How big is a giant otter compared to a human?

Very close to an adult’s height. The International Otter Survival Fund gives up to 2 m (6.5 ft) and about 32 kg (70 lb), almost double the length of the marine otter. Measured animals are often a little smaller: a study of 15 giant otters in Brazil recorded maximums of 1.63 m (5 ft 4 in) and 28.8 kg (63 lb). It swims by paddling with its four feet or by undulating its broad, flat tail, which earned it old names such as the flat-tailed otter. Each animal has its own pattern of pale markings on the throat, and researchers film them to tell individuals apart.

Where do giant otters live?

Only in South America. The IUCN lists the species as native to Peru, Bolivia, Brazil, Colombia, Ecuador, French Guiana, Guyana, Paraguay, Suriname and Venezuela, while its presence in Argentina and Uruguay is uncertain. It lives in the lowlands, below 1,000 m (3,300 ft), where each family defends a stretch of river or a whole oxbow lake, with dens dug into the bank and cleared campsites on shore. In Peru that means the Amazon rainforest east of the Andes; in the southeast, the protected areas of Manu and Tambopata hold some of the country’s best-known families.

Where to see giant otters in Peru

Peru’s protected areas service, SERNANP, highlights three oxbow lakes in the southeast where visitors can watch giant otters. These are the places our groups visit:

From Puerto Maldonado, SERNANP lists about 30 minutes by river and a 3 km (1.9 mi) walk to the Sandoval sector, where an interpretation center stands next to the checkpoint. The Manu lakes are deep inside the Reserved Zone, which can only be visited with an authorized operator. For the rest of the wildlife of each area, see wildlife in Manu or compare Manu vs Tambopata.

How many giant otters live in Manu?

The Frankfurt Zoological Society has studied the giant otters of Manu since around 1990, identifying each animal by the markings on its throat. In its 2002 census of 21 oxbow lakes in the Manu Biosphere Reserve, the team counted 66 different giant otters: 12 family groups and 3 solitary animals. Groups averaged 5.3 members, the largest had 12, and that year the families raised at least 15 cubs.

Are giant otters dangerous?

Giant otters are top predators of the lakes and very vocal, with nine different calls that probably serve as alarms and contact calls, so a family makes a lot of noise when something approaches. In the wild they keep away from people, and the real risk runs the other way: boats, noise and crowding stress the families, and researchers in Madre de Dios have reported groups reacting nervously even on lakes where tourism is managed. When you watch them:

• Keep your distance and stay quiet. Let the otters decide how close they come.
• Use only authorized boats. At Salvador only the catamaran is allowed, and at Sandoval visitors travel in boats run by local people and lodges.
• Do not swim in the lakes and never feed the animals.
• Bring binoculars. Your guide carries a spotting scope; see our Amazon packing list.

Why are giant otters endangered?

Hunting for their pelts drove giant otters out of much of their range, and they are still hunted illegally for them; the IUCN moved the species from Vulnerable to Endangered in 2000. Its latest assessment, from 2020, keeps it as Endangered with a decreasing population. Today the main threat is the loss and degradation of its rivers and lakes; in Madre de Dios, researchers are surveying oxbow lakes in areas damaged by gold mining to see whether otters return. Protected areas such as Manu and Tambopata, where the lakes are monitored and tourism has rules, are among the species’ safest refuges in Peru.

Sources

• IUCN Red List: Giant Otter, Pteronura brasiliensis (Endangered, assessed 7 March 2020; population trend; native countries; elevation)
• Animal Diversity Web (University of Michigan): Pteronura brasiliensis (average weight, groups, diet, reproduction, calls, swimming, pelt hunting)
• International Otter Survival Fund: Giant Otter fact sheet (length, weight, group size, diet, hunting)
• Rosas et al., Body weight-length relationships in giant otters, INPA repository (measurements of 15 otters)
• SERNANP: Tambopata National Reserve and Manu National Park (Sandoval, Otorongo and Salvador lakes)
• Groenendijk & Hajek (2003), Giant Otter Project in Peru, IUCN Otter Specialist Group Bulletin 20(1) (Manu census, IUCN uplisting, reactions to tourism)
• San Diego Zoo Wildlife Alliance: Looking for giant otters in mined areas of the Peruvian Amazon

Updated October 2026.