Hydro-electric power is one of those things that seems like it’s been around forever, but hasn’t been talked about very much since the emergence of geothermal, solar and wind. Basically, hydro-electric takes falling water (like at Niagara Falls, or the Hoover Dam) and turns the motion into electricity.
So much energy can be produced by a hydro-electric turbine with very little effort or cost to maintain the system, making this resource one of the most beneficial of all alternative energy sources. In fact, the time-tested system is so reliable, it’s amazing that more cities with access to fast flowing water haven’t begun taking advantage of hydro-electric.
For more details on the inner workings of a dam or hydro-electric station, watch a video in the replies.