It’s been known that in the 20th century the US built several dams across the West to direct and conserve river water, generate electricity, and store water in reservoirs for city and farm use. VOX.com says, “This intricate system is why metropolises like Los Angeles, Las Vegas, and Phoenix have been able to survive in what’s basically a desert. Large-scale farming is really only possible in California’s Imperial Valley or central Arizona because of these dams but now they are strained by Severe Drought.”

Why are United States dams so important to Americans and environmental sustainability?

Rising population and demand, as well as California’s several years of drought have strained this system severely.

Here’s a terrific interactive map created to show how the Western states have decreased in water supply over the years.

Results show that many state reservoirs fell below 50 percent during the recent drought. An example of this is Lake Mead–a key reservoir that helps supply 25 million people in Nevada, AZ, and California. This last May 2016, marked its record low level of water. If water levels at Lake Mead continue to plummet, the federal government could declare an official water shortage and force cutbacks. Read more about Lake Mead, Hoover Dam, and Lake Powell.