A Bottom-Bound Way to Move
A hippo’s heavy body does not stay buoyant enough for ordinary surface swimming. Instead, it travels underwater by pushing off the riverbed with its strong legs. The movement resembles a slow-motion gallop: the animal bounds forward, briefly lifting from the bottom before landing and pushing off again.
That is why “running underwater” is more than a colorful description. The riverbed supplies the firm surface a hippo needs to drive itself forward. In deeper water, where it cannot reach the bottom, this usual mode of travel is limited.
Breathing Without Breaking the Rhythm
Hippos can remain submerged for several minutes, but they must return to the surface for air. Their nostrils sit high on the head, so a hippo can breathe while keeping most of its body in the water. It closes its nostrils underwater and opens them again at the surface.
The return to air does not require the animal to be fully alert. A sleeping hippo can surface and breathe automatically, then sink again. Its breathing cycle can continue while the rest of the animal remains asleep.
The Riverbed as a Route
This way of moving suits an animal that spends much of its time in water but is not built to paddle like a typical swimmer. Rather than crossing a river by floating and stroking at the surface, a hippo can make its way along the bottom, repeatedly pushing off the ground and rising only when it needs air. Even at rest, it may be following that same underwater routine.
