It can change almost overnight from a muddy trickle into the sort of torrent that carved the Grand Canyon. Settlers complained that the waters of the Colorado River, rich with rust-colored sediment, were “too thick to drink and too thin to plow,” even as its currents nourished the rapid growth of an entire quadrant of the country. With 30 million people in seven states and Mexico relying on it, the Colorado is the most contested river system in North America. In 1893, Major John Wesley Powell, the first explorer of the Colorado, warned against hopes that the unpredictable desert river could satisfy all of the demands that would be made of it: “You are piling up a heritage of conflict and litigation over water rights, for there is not sufficient water to supply these lands.” He was onto something. Harnessed for hydroelectric power and pumped through hundreds of miles of aqueduct to L.A., Phoenix, and Denver, the river is usually (except in major flood years) used up before reaching its outlet at the Sea of Cortez in Mexico.
In that way the Colorado is also perhaps the most micromanaged waterway we have. And to a certain extent, the most mismanaged. The entire system that determines how much water can be taken from the Colorado rests on a colossal error: In 1922, when its waters were divvied up among the states, the Colorado was enjoying its wettest ten-year period on record. Estimating its annual flow, the states used a number—16 million acre-feet—that they thought was conservative, but it turned out to be wildly high. The average flow in the decades that followed has been closer to 12 million acre-feet. Since 2002, we’ve been using a million acre-feet more than the river contains—by sucking down the desert reservoirs of Lake Powell and Lake Mead, which are now less than half full and falling. Adding to overuse are a lack of rain and snow (2012 and 2013 are the fifth and fourth driest years on record) as well as evaporation (a quantity of water greater than urban Southern California’s yearly allotment simply disappears from the reservoirs each year). At the current pace forecasters say Lake Mead may fall to 1,075 feet above sea level (154 feet below its high-water mark), triggering water cutbacks to Las Vegas, Phoenix, and Tucson. One study gives a 50-50 chance that Lake Mead will be empty by 2021—better than your chances of winning in any Vegas casino.