Until the 20th century, the Colorado River moved freely through the West, from forested Rocky Mountain headwaters through canyons, deserts, and lush wetlands and then out to sea. But by 1922, as cities and farms expanded, the seven states in the river basin divvied up its flow, and a growing number of dams and irrigation projects tamed its majesty. Today more than 40 million people rely on its water. These demands are now too great for what the Colorado River can supply.