To live comfortably, humans need a reliable source of fresh water. Many population centers depend on rivers for a steady water supply. In the arid climate of the western United States, though, water can be scarce. Long periods without rain can cause rivers to dry up, interrupting the supply of water. People learned long ago that by building a dam across a river, they could hold back some of the river's water and store enough to meet their needs through a dry season. Land upstream of the dam had to be abandoned because it flooded, and the river would change downstream too, because it received less water and fewer floods. But building a dam helped ensure a steady water supply.

Early in the 1900s, the limiting factor for development of land in the western United States was the availability of water. Damming the Colorado River, which drains snowmelt and rain from the western side of the Rocky Mountains, was seen as a solution. In 1922, the Colorado River Compact outlined a plan to build a series of dams along the Colorado River that would control floods and ensure a steady water supply for southwestern states.