“Animals with pale skin and little fur are most at-risk for sunburns. A few examples are pigs, rhinos, and elephants.” Source

This is why you are elephants cover their backs in mud, it acts as a sunscreen and also helps to keep them cool.

And now I’ve got to be the tertiary guy and point out that if the flow rate into a reservoir is low enough, and the surface area of the lake large enough, evaporation can control the water level. See: aral sea.