How is a hydro electric power station built?

Answer 1

A dam is built, normally across a river but sometimes across a lake or even the sea, in a suitable place. Anyway, once the dam is built, water cannot pass through so it builds up on one side - so that you have a dam with a high water level on one side and no water on the other. There are passages built into the bottom of the dam which contain turbines, and once the water level reaches a sufficient height these passages are opened and water can pass through from the 'high level' side to the 'no water' side (obviously). As the water goes through the passages it spins the turbines which in turn spin electrical generators, creating electricity.