You will also see kayakers paddling upstream against the current. This is as much a mental exercise as it is one of brute strength. In fact, all playing is really just a form of exercising the fundamental skills that you will need to help you out in bigger, badder water. In order to attain, one uses the features of the river to get from point A to point B. Oftentimes, to the unschooled observer, the odds of getting from A to B seem to be zero. Both of these activities work on boat control and balance.
Balance is an absolutely essential key to kayaking.
It is the foundation of agility. It is not very difficult to sit flat on the water and make a strong powerful paddle stroke. It is an entirely different task, however, to lean your boat 45 degrees downstream and then make a strong powerful paddle stroke while maintaining that angle. While your arms and shoulders reach through the stroke you have to make a hundred minute and subtle adjustments to compensate for the shifting center of gravity. It is a learned skill.