Hippos are large amphibian creatures that can weight up to around 10,000 lbs. They spend the large majority of time in water to keep cool from the sun. They are very territorial, and heavily aggressive towards anything they feel is threatening. Case in point, this boat. Notice that as the boat approaches a Hippo, it must veer course and accelerate in order to ovoid a confrontation, but the Hippo manages to get within a few feet of the boat, almost reaching the back of it.