All mammals generate heat through metabolism. Elephants have many different ways of controlling their body temperature. Elephants being big and active generate a lot of heat. This, added to the hot summer sun their body temperature can rise rather quickly. They have a different mechanism that they use to help them cool down, from ear flapping to mud bathing are all great ways to dissipate heat.
But the most enjoyable is probably a good old fashion swim. Yes, elephants are very good swimmers and they thoroughly enjoy the water. It not only cools them down but takes some of the weight of their feet. They can sometimes play for hours in the water doing somewhat acrobatic displays which are of course a sight to see. You will find them play fighting or even splashing as they fall over backwards.
Their amazing agility becomes evident. To see how swiftly they can move and push and play is a humbling experience. All of this just to relax and dissipate heat while having a bit of fun. This is, however, a great way to bond and strengthen relationships within the herd.