The United States has approximately 75,000 dams. Some are small, and some are huge. Many of these date back to the nineteenth century, when water provided a significant portion of the nation's power. Others have been built more recently.
The League of Women's Voter's “Green Issues Summer Movie Series” sponsored an August 12 showing of "DamNation", a film that asks us to consider whether all of these dams are still necessary. “DamNation” won twenty film awards in 2014- 2015, including the Environmental Film Festival in the Washington DC “2014 Environmental Advocacy Award” and the International Wildlife Film Festival “2014 Best Conservation Film.”
Dams have been built for many reasons, including hydropower, flood control, irrigation, and transportation. River barges that can't negotiate rapids can go up and down the river via locks. Without water control the population of the West could not be as high as it is today.