Hydropower uses the energy of flowing water to spin a turbine and generate electricity.  Run-of-the river-hydroelectric generators are among the greenest and most affordable sources of electricity in the world. The use of hydropower to generate mechanical energy dates back hundreds of years to early saw and grain mills. In the 1800s many Vermont dams were built to harness water’s power for saw and grain mills, with settlement patterns following rivers for this reason. The late 1800s saw new dams being built, and old ones converted to pair running water with electrical generators, as the first hydroelectric power plants came on line in Vermont and throughout America.  Many hydro generators in Vermont are now more than 100 years old, requiring only refurbishment of the turbines and generators about every 30 years.