Here's why:
* They are semi-aquatic: Hippos are adapted to both water and land. They spend their days in rivers, lakes, and swamps, cooling off and protecting themselves from predators.
* They need to come ashore: Hippos need to come onto land to graze on grass at night.
* They give birth on land: Female hippos give birth to their calves on land, typically near the water.
* They are mammals: Like all mammals, hippos breathe air and give birth to live young.
So while they live primarily in water, hippos are land-based mammals who need to come ashore for various activities.