Hydroelectric dams helped power the nation's economy in the early 1900s, increasing the power supply for communities and mitigating the risk of seasonal flooding. Water districts built massive dams to store water for irrigation and to meet the demands of a growing urban population. The 1950s and 60s saw the peak of dam construction in America. However, the era of dams plugged rivers, submerging scenic and culturally significant valleys and halting important natural processes, such as downstream sediment movement and upstream fish migration. As the public became aware of the negative impacts caused by obstructing the natural free-flow of our rivers, a movement was afoot to defend the nation’s remaining pristine waterways.