How?

 Hydroelectricity is derived from the potential energy that water has when it is at a height above sea level. One side of the dam holds backwater at a high level and the other side has water flowing at a low level. As the water falls to the lower level, some of the energy can be transformed into energy by being directed through turbines. A generator produces electricity. The generators in a hydropower station are powered by the turbines, which are powered by the falling water. As the generator turns, it produces electricity. This is called hydroelectricity because its source is water