If you have ever seen a giant otter glide past in an Amazon channel, the first thing that strikes you is the sheer length of the animal. So how big does the giant otter actually get, and what makes it the largest otter on Earth?
How long is a giant otter?
A giant otter (Pteronura brasiliensis) can reach up to about 1.8 metres, roughly 6 feet, from the tip of its nose to the end of its tail. That long, muscular tail accounts for a large share of the total and works like a rudder and propeller in fast water. No other otter species grows as long, which is why the giant otter is described as the longest member of the weasel family, the Mustelidae.
How much does a giant otter weigh?
Weight is where the giant otter and the sea otter run close. A male giant otter typically weighs around 26 to 32 kg, while females weigh roughly 22 to 26 kg, about the size of a medium to large dog. The sea otter can match or exceed that weight but is shorter in overall length, so the two share the title of largest otter from different directions: the giant otter wins on length, the sea otter often on bulk.
Why is it so big?
Size pays off for a cooperative river predator. A long, streamlined body lets the giant otter accelerate after fast prey such as cichlids, characins and catfish, and an adult eats roughly 3 to 4 kg of fish a day to fuel that effort. Being large and living in groups of three to eight also makes the giant otter a formidable apex predator that can stand its ground against caimans.
How does it compare to other otters?
- Giant otter: up to 1.8 m, 22 to 32 kg, the longest otter.
- Sea otter: shorter overall but heavy bodied, the bulkiest otter.
- Neotropical otter: a close South American relative at only about 0.9 to 1.3 m.
- Eurasian otter: around 1 to 1.3 m, far smaller than its giant cousin.
For the full set of measurements, lifespan and biology, see our giant otter species guide. The species is Endangered, and the rivers where these big otters thrive are shrinking, so backing habitat protection in their last strongholds quietly helps keep room for the world's longest otter.
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.
