Hippos spend a lot of time in the water, and although many people think that they swim, they actually don't.
Hippos use a method to move through the water that involves "hopping," or allowing themselves to sink down to the bottom of a body of water so that they can kick off from the floor with their tremendously-powerful rear legs.
The result is that the hippo appears to move very quickly through water, at about 7 miles per hour. It's not actually swimming; hippos are terrible swimmers, but it does allow the hippo to effectively cross water and get from point A to point B.
When one comes after you while doing this ‘water hopping' technique, you're in trouble. Since hippos are territorial, you should be aware of your surroundings and realize that they're coming after you to get rid of you. Many people die on an annual basis due to hippo attacks.