Hippos are definitely adapted for life in the water and are found living in slow-moving rivers and lakes in Africa. With their eyes, ears, and nostrils on the top of the head, hippos can hear, see, and breathe while most of their body is underwater. Hippos also have a set of built-in goggles: a clear membrane covers their eyes for protection while still allowing them to see when underwater. Their nostrils close, and they can hold their breath for five minutes or longer when submerged. Hippos can even sleep underwater, using a reflex that allows them to bob up, take a breath, and sink back down without waking up.
Yet despite all these adaptations for life in the water, hippos can't swim—they can't even float! Their bodies are far too dense to float, so they move around by pushing off from the bottom of the river or simply walking along the riverbed in a slow-motion gallop, lightly touching the bottom with their toes, which are slightly webbed, like aquatic ballet dancers.
Baby hippos' are very cute, but despite this, they grow up to be among the most dangerous and aggressive of all mammals. Their canine and incisor teeth grow continuously, with canines reaching 20 inches (51 centimeters) in length. Hippo males especially use their canines for fighting. To ward off enemies, a hippo may yawn, scoop water with its mouth, shake its head, rear up, lunge, roar, grunt, chase, and make a loud wheezing sound, all of which are threat displays. A hippo can kill people if it's provoked or feels threatened. But the impressive tusks and canine teeth are used mainly for defense or fighting with other hippos.