Not only are individual hippos dangerous for the reasons Irwin stated, but they are doubly threatening in a group situation. In a herd, the highly territorial animals are easily agitated and are liable to act out. Add the alpha bull male to the volatile mix, and it can make for a perilous situation. Indeed, this was one scene that the experienced naturalist was very vocal about his wish to avoid.
To underline the validity of Irwin’s point, consider this highly revealing World Health Organization statistic from 2016. Although 100 people are killed by lions each year in Africa, almost 3,000 people lose their lives to hippo attacks. It is little wonder Irwin was so skittish around the water-dwelling behemoths.