The giant otter (Pteronura brasiliensis) is the largest, loudest and arguably the most charismatic otter on the planet. Locals across the Amazon call it the "river wolf" for good reason. Here are eleven facts that capture what makes this endangered predator so extraordinary.
11 things to know about the giant otter
1. It is the longest otter on Earth
A full-grown giant otter can measure up to 1.8 metres from nose to tail tip, making it the longest member of the entire weasel family, the Mustelidae.
2. Every otter has a fingerprint on its throat
Each animal wears a unique cream-coloured patch of fur on its throat. The markings are so distinctive that field researchers use them, like fingerprints, to identify and track individuals across years.
3. It hunts by daylight
Unlike many predators, the giant otter is diurnal, relying on sharp eyesight to chase fish through shallow, sunlit water.
4. It is the noisiest otter alive
Giant otters are intensely vocal. A peer-reviewed study of their calls documented a rich repertoire of snorts, screams, hums and warning barks; popular accounts often cite at least nine distinct vocalisations used to coordinate the group.
5. Families raise pups together
A typical group of three to eight is built around one breeding pair, and older siblings help feed and guard the youngest pups.
6. It eats several kilograms of fish a day
An adult puts away roughly 3 to 4 kg of fish daily, mainly cichlids, characins and catfish, and will also take crabs, snakes and the occasional small caiman.
7. It is a true apex predator
Few animals threaten a healthy adult, and groups have been recorded driving off caimans many times their size.
8. Its fur is almost waterproof
Dense, velvety underfur traps a layer of air and keeps the skin dry, which is exactly the quality that made it a target for hunters.
9. Hunting nearly wiped it out
From the 1940s to the 1970s tens of thousands of pelts were traded internationally until CITES listed the species on Appendix I, banning commercial trade.
10. It is now Endangered
The IUCN's 2021 assessment lists fewer than 5,000 mature individuals in fragmented, declining populations.
11. It cleans up rivers it can no longer always live in
As a top predator it helps balance fish populations, yet gold-mining and mercury pollution are poisoning the very rivers it depends on. You can read the full story in our giant otter species guide. Brazil and Colombia hold some of its last strongholds, and supporting river-habitat protection there is one quiet way to help these families hold on.
Read the full Giant otter wildlife guide for the facts, IUCN status and conservation context — or donate to WARN to help fund the local partners protecting this species.
