Hydro power must be one of the oldest methods of producing power. No doubt, Jack the Caveman stuck some sturdy leaves on a pole and put it in a moving stream. The water would spin the pole that crushed grain to make their delicious, low-fat prehistoric bran muffins. People have used moving water to help them in their work throughout history, and modern people make great use of moving water to produce electricity.

Advantages to hydroelectric power:
Fuel is not burned so there is minimal pollution
Water to run the power plant is provided free by nature
It's renewable - rainfall renews the water in the reservoir, so the fuel is almost always there