Hippos look slow on land but they are surprisingly fast. They can run at 30 kilometres an hour for short bursts - faster than a human can sprint. Underwater, they don't actually swim. They walk along the bottom of the lake, pushing themselves with their toes. Their eyes, ears and nose are all on top of their heads so they can keep watch while the rest of their body stays cool below the surface.
Hippos spend the day in water to keep their skin from drying out in the strong African sun. Their skin also produces a special pinkish-red oil that works like sunscreen and bug spray rolled into one. People used to think hippos were 'sweating blood', but it is really a clever skin product made by their bodies.
At night, the whole group climbs out of the water and walks to nearby grasslands to feed. A single hippo can eat about 40 kilograms of grass in a night. The same paths get used by hippo families for many generations - they become smooth grooves in the earth, like little hippo motorways.
Baby hippos are born underwater. Within a minute, mum nudges them to the surface for their first breath. They can swim immediately. The babies often ride on their mothers' backs in deeper water and play together in the shallows, splashing and chasing each other.