The water is collected behind a dam in a reservoir. Williston Lake reservoir in this picture is covered with snow. The water then flows through ten freestanding intake gates. You can see just one of the 10 pen stocks in the diagram. The falling water turns a turbine inside the underground powerhouse.
Hydroelectricity requires water to fall on a turbine and make it rotate.
Each turbine has a great spiral shaped chamber called a scroll case that directs the water into the turbine blades. This photograph shows the cranes that are used to lift the generating units up so that they can have maintenance work done on them. This generating unit has the cover taken of and soon will lifted out using the large cranes. The electricity is taken to the users by transmission lines. Water is discharged from the turbines from shaped draft tubes.