The orca is 3x heavier and a superior aquatic fighter — the hippo's river dominance doesn't translate to the ocean.
In a river, the hippo is incredibly dangerous. In the ocean, the orca is the apex predator. Since realistic encounters would happen in coastal or estuarine waters where both could operate, the orca's aquatic superiority gives it the decisive advantage.
The orca is 3x heavier (12,000 lbs vs 4,000 lbs), far faster in water, and hunts in coordinated pods. A single orca could ram the hippo with devastating force, and its intelligence far exceeds the hippo's.
The hippo's jaws are terrifying, but the orca's echolocation means it's never surprised. It can attack from angles the hippo can't defend — below, behind, or at speed from distance.
The hippo's 1,800 PSI bite through massive canines is devastating at close range. In shallow water where it can touch bottom, the hippo's aggression makes it dangerous.
3:1 weight advantage, vastly superior aquatic speed, echolocation for perfect awareness, and intelligence that far exceeds the hippo's. Orcas have killed much larger and better-armed aquatic opponents.
The orca wins in any open water scenario. The hippo's river dominance doesn't translate when facing the ocean's apex predator at 3x its weight.
Hippopotamus also fights