Freshwater
Adapted to inland rivers, creeks, and lakes, pumping out excess water through specialized kidney filtration.
Cottonmouth
A swamp pit viper that warns with a wide-open white mouth and hunts on land and in water.
Duck-Billed Platypus
An egg-laying mammal with venomous spurs and an electric sense in its bill, once thought to be a taxidermist's hoax.
Electric Catfish
A night hunter of the Nile and Lake Chad wrapped in a living battery, from a genus that can discharge up to 350 volts.
Emperor Dragonfly
A big dragonfly whose larva fires a hooked mouthpart at prey, too fast for a water flea to escape.
Eurasian Beaver
Europe's orange-toothed dam builder, hunted to near extinction, then counted at over 1.5 million across Europe by 2012.
Eurasian Otter
Whiskers that sense a fish moving through the water, a scent-marked calling card called a spraint, and a river range that stretches from Britain to Japan.
European Eel
A river fish thought to spawn only in the Sargasso Sea, after a 5,000 to 10,000 km migration, though its spawning has never been observed.
European Medicinal Leech
A three-jawed pond blood-drinker that can go 12 to 18 months between meals and was overharvested for medicine.
Gharial
The narrow-snouted river crocodilian with up to 110 razor-sharp teeth, whose males grow a bulbous nasal resonator that buzzes as they exhale.
Giant Freshwater Stingray
The 300-kilogram Mekong river phantom with a barbed tail spine and the record for the largest freshwater fish ever caught and officially recorded.
Giant River Otter
The biggest of all the otters, the Amazon's "river wolf" has jaw leverage that should favor speed and an adult vocabulary of 22 distinct calls.
Giant Water Bug
A big water bug that stabs fish and tadpoles with its beak, and is drawn to lights.
Glass Frog
See-through belly skin that shows off a beating heart, green bones, and a liver that can hide most of the frog's red blood cells.
Great Cormorant
A fish-chasing diver with wettable feathers, which has to hang out its wings to dry.
Great Crested Grebe
The diving bird whose courtship runs from paired head-shaking to a breast-to-breast 'Penguin-dance,' and whose chicks ride on their parents' backs.
Green Anaconda
Up to 550 pounds of camouflaged ambush predator, with eyes and nostrils on top of its head, that kills with suffocating coils.
Green Drake Mayfly
A burrowing mayfly that finds rivers by their polarized glint, and lands on smooth black plastic too.
Grizzly Bear
The most distinctive shoulder hump of any brown bear, claws built for digging, and a fall feeding binge of about 20,000 calories a day.
Hellbender
North America's biggest salamander, breathing mostly through its own wrinkled skin instead of its lungs.
Hippopotamus
A one-and-a-half-tonne river giant that walks the riverbed instead of swimming, and oozes its own sunscreen.
Hoatzin (Stinkbird)
A cow-style fermenting crop, wing-clawed chicks that swim from danger, and a place on the bird family tree debated since it was described in 1776.
Hydra
A small freshwater polyp whose death rate in lab studies stayed flat as it got older.
Jaguar
Skull-piercing jaws, a powerhouse swimmer, and the largest cat in the Americas.
Japanese Giant Salamander
Up to five feet of living river boulder that breathes through its skin, hunts by smell and vibration, and gives off a peppery smell when stressed.