10 Fearsome Creatures of the Amazon River

The Amazon rainforest is a vast ecosystem, home to creatures as bizarre and awe-inspiring as the jaguar, the venomous dart frog, and the Jesus lizard. However, it’s not just the animals that roam, swing, and slither through the trees that make this place extraordinary. Beneath the waters of the Amazon River—the largest river on the planet—live creatures so incredible and frightening, they make Jaws seem like a peaceful day at the beach.

10. Black Caiman

A black caiman is essentially an alligator on a power boost. They can reach lengths of up to six meters (20 feet), with skulls larger and more robust than those of Nile crocodiles. As the ultimate predator in the Amazon's waters, they reign supreme in the river, devouring almost anything they encounter—including piranhas, monkeys, perch, deer, and even anacondas.

And yes, they do attack humans. In 2010, a biologist named Deise Nishimura was attacked by a caiman while she was cleaning a fish on her houseboat. Although she managed to fend it off, it took one of her legs in the process. This particular caiman had been lurking beneath her houseboat for eight months, seemingly waiting for the perfect moment to strike.

9. Green Anaconda

Sticking with the theme of massive reptiles, the world’s largest snake calls the Amazon home: the anaconda. While reticulated pythons grow longer, green anacondas are far heavier; females, typically larger than males, can weigh up to 250 kilograms (550 lbs), stretch to 9 meters (over 29 feet) in length, and have a diameter of 30 centimeters (12 inches). These giants aren’t venomous, but rely on their immense strength to squeeze and suffocate their prey, which includes capybaras, deer, caimans, and even jaguars. Preferring the shallower waters where they can ambush their prey, they tend to inhabit the tributaries of the Amazon rather than the main river itself.

8. Arapaima

The arapaima, also known as “pirarucu” or “paiche,” is a colossal carnivorous fish that inhabits the Amazon and nearby lakes. Shielded by armor-like scales, they aren’t deterred by living in piranha-infested waters—and they’re quite effective hunters themselves, feeding on fish and sometimes birds. Arapaimas stay near the surface, as they need to breathe air in addition to absorbing oxygen through their gills, producing a distinctive coughing sound when they surface. These fish can grow up to 2.7 meters (nine feet) long and weigh as much as 90 kilograms (200 lbs). They’re so ferocious that even their tongue is armed with teeth.

7. Giant Otter

Leading the “exactly what it says on the tin” category are the giant otters, who, as their name implies, are truly massive otters. They are the largest members of the weasel family, with adult males growing up to two meters (over six feet) long from head to tail. Their diet is mainly composed of fish and crabs, which they hunt in family groups ranging from three to eight members, and they can consume up to four kilograms (nine pounds) of seafood each day. Don’t be deceived by their adorable appearance, though—they’re formidable opponents for the other creatures on this list, with groups observed killing and consuming an anaconda. They can even stand their ground against caimans. One family was seen devouring a 1.5-meter (five-foot) caiman in about 45 minutes. Despite their population declining due to human activities, they remain one of the Amazon rainforest’s most efficient predators, earning them the local moniker “river wolves.”

6. Candiru

The Amazon is home to more than just giants, and its smaller creatures are equally terrifying, particularly if you believe the myths surrounding them. Candiru are tiny, parasitic freshwater catfish infamous for their ability to launch themselves into the urethra of anyone foolish enough to urinate in the river, becoming lodged in the urinary tract due to the spines along their backs. While confirmed cases are rare, and some debate whether such incidents even occur, there is at least one documented case of a man needing surgery to remove a candiru from his urethra, which had also attempted to burrow into his testicles. However, the candiru typically preys on fish, using their spines to attach to the larger fish’s gills and feed on their blood.

5. Bull Sharks

Although bull sharks are primarily known as ocean-dwelling saltwater creatures, they are equally at home in freshwater. They’ve been spotted as far into the Amazon as Iquitos in Peru, nearly 4,000 kilometers (2,500 miles) from the sea. Their specialized kidneys can detect changes in the salinity of the surrounding water and adjust accordingly. You definitely wouldn’t want to encounter one of these in the river; they commonly grow to 3.3 meters (11 feet) in length, with some reports of sharks weighing as much as 312 kilograms (690 pounds). Like most sharks, they have multiple rows of sharp, triangular teeth and incredibly powerful jaws, capable of delivering a bite force of 589 kilograms (1,300 pounds). Bull sharks are notorious for being one of the most frequent attackers of humans (along with tiger sharks and great whites). Their habit of living near populated areas has led many experts to label them as the most dangerous sharks on the planet.

4. Electric Eels

Electric eels are more closely related to catfish than true eels, but you probably wouldn’t want to get close enough to one to learn that firsthand. They can grow up to 2.5 meters (eight feet) long and generate electric shocks from specialized cells called electrocytes that line their flanks. These electrical charges can reach up to 600 volts, which is five times more powerful than a standard American electrical socket, and enough to knock a horse off its feet. While a single shock won’t usually kill a healthy adult human, repeated shocks can lead to heart failure or respiratory failure, and it’s common for victims to be stunned and drown after an eel attack. Many of the mysterious disappearances in the region have been attributed to eels that incapacitate their prey and leave them to drown in the river. Fortunately for humans, electric eels, though carnivorous, generally feed on fish, amphibians, birds, and small mammals. They hunt by emitting small 10-volt shocks from their electrocyte cells to locate their prey, before using larger shocks to stun or kill them.

3. Pacu

One creature that is definitely more frightening for men than women, the pacu is a much larger cousin of the piranha, distinguished by its human-like teeth. Unlike most of the animals on this list, the pacu is omnivorous, with a diet that includes fruit and nuts. However, for some pacu, ‘nuts’ may not just mean what falls from trees. Yes, indeed: There are reports of pacu occasionally biting off the testicles of male swimmers, with incidents in Papua New Guinea where the fish reportedly mistook genitalia for a tasty treat. And don’t worry if you can’t get to the Amazon to observe these manhood-munching creatures, as they are already spreading into Europe.

2. Payara (Vampire Fish)

Anything called ‘vampire fish’ is bound to send chills down your spine (even after Twilight), and payara certainly live up to that fearsome name. These creatures are ferocious hunters, capable of swallowing prey that is up to half their size. Given their potential to grow to 1.2 meters (four feet) in length, that’s quite impressive. A significant portion of their diet consists of piranhas, which gives you an idea of how formidable these fanged monsters really are. Their name comes from the two sharp tusks protruding from their lower jaw, growing up to 15 centimeters (six inches), which they use to viciously impale their prey after an aggressive lunge. Their fangs are so large that their upper jaw has special holes to avoid impaling themselves.

1. Red-Bellied Piranhas

The iconic terror of the Amazon River, so feared they’ve inspired several dubious Hollywood films, red-bellied piranhas are actually mostly scavengers. That doesn’t mean they won’t attack healthy prey, though—considering they can grow over 30 centimeters (12 inches) long and travel in large, menacing groups, they’re a force to be reckoned with. Like all piranhas, their sharp teeth are arranged in interlocking rows on both their top and bottom jaws, making them perfect for tearing flesh. Their notorious reputation largely stems from their ‘feeding frenzies,’ in which they quickly devour their unfortunate victims down to the bone. Such attacks, however, are rare and usually occur due to starvation or provocation.