A manatee can grow up to 4 metres long and weigh as much as a small car. Despite their size, they are very gentle. They eat only plants - water grasses, leaves and any greenery they can find in the river. A grown-up manatee eats around 50 kilograms of plants every single day - the weight of a small adult human.
Manatees have to breathe air, but they can hold their breath for up to 20 minutes while they're feeding underwater. They come up to the surface, take a quick breath, and slide back down. When they sleep, they actually float just under the water and rise up every few minutes to breathe without fully waking up.
Their closest living relatives are not whales or seals - they are elephants. If you look at a manatee's foot bones, they look surprisingly similar to an elephant's. Scientists believe both animals share a great-great-grandparent that lived around 60 million years ago.
African manatees are quite shy. They live in muddy rivers, so even the people who know them best mostly see ripples on the water rather than the whole animal. They almost never come on land. Today they are protected in Nigeria because their slow, gentle lives can make it hard for them to stay safe near busy rivers.