Why do hippopotamuses need to return to water after basking in the sun?

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A hippopotamus stands at the edge of a watering hole, with several other hippos partially submerged in the water, surrounded by green vegetation in Botswana, Africa. — hippopotamus The word *hippopotamus* is Greek for “river horse,” which reflects their behavior: they are often seen basking on the banks or sleeping in the waters of rivers, lakes, and swamps across Africa. They favor shallow areas where they can sleep half-submerged, though these places can become quite crowded—as many as 150 hippos may use one pool in the dry season.

Hippopotamuses must return to the water after basking in the sun for two primary physiological reasons:

Temperature Regulation: Hippos do not sweat, so they must retreat to the water to keep their bodies cool.12
Hydration: They lose water rapidly through their skin and will become dehydrated without periodic dips in the water.12

While basking, hippos are protected from the sun by a natural secretion from their skin glands. This oily, reddish or pinkish substance—often mistaken for blood—acts as a sunblock by filtering out ultraviolet radiation.12