Twelve hippo facts, fact-checked
The hippopotamus is a semi-aquatic giant whose nearest relatives are out at sea. Full profile in our hippopotamus guide.
1. They cannot swim
Too dense to float, hippos walk and bound along the riverbed, pushing off the bottom to surface.
2. Their closest relatives are whales
Hippos and cetaceans share a common ancestor, making a whale a closer relative to a hippo than a pig is.
3. They sweat red
A secretion often called blood sweat is neither blood nor sweat. It is an oily fluid that acts as sunscreen and antibacterial agent, turning red then brown on exposure.
4. They surface to breathe while asleep
The reflex works without waking them.
5. They are Africa's most dangerous large animal
Highly territorial in water and unpredictable on land, hippos are responsible for more human deaths than lions or crocodiles.
6. Their jaws open about 150 degrees
A gape used for display as well as combat, backed by canines that can exceed 50 cm.
7. They are grazers
Feeding on land at night, taking around 40 kg of grass — modest for their size, since floating conserves energy.
8. Their dung fertilises rivers
Nutrient transfer from land to water underpins fish populations in many African river systems.
9. Calves can suckle underwater
Closing ears and nostrils to nurse below the surface.
10. They communicate above and below water simultaneously
Calls carry through both air and water at once, which is very unusual.
11. They are Vulnerable
Habitat loss, water extraction and hunting for meat and ivory canines drive decline.
12. Their teeth are traded as ivory
Hippo canines are a legal-grey ivory substitute, and demand rose as elephant ivory controls tightened.
Read the full hippopotamus wildlife guide for IUCN status, population context and sources — or donate to WARN to help fund the partner teams protecting wildlife on the ground.
