Users of Colorado River water below Lake Mead — including the cities of Phoenix, Los Angeles, Las Vegas (collectively referred to as the “lower basin”) — rely on the reservoir as a lifeline. The people in the lower basin exist partly at the mercy of what happens in the upper basin, an area encompassing the snowcapped peaks of Wyoming, Utah, Colorado, and northern New Mexico, the source region of the river.
Big water users in the upper basin — Salt Lake City, Denver, Albuquerque, among others — are also getting nervous because snowpack in the Rockies has been dwindling, and there’s no physical way for them to store the water they depend on. There are no big reservoirs in the Rockies.
In recent weeks, tensions are rising after states in the upper basin sent a strongly worded letter to one of the river’s biggest users, the Central Arizona Water Conservation District, or CAWCD, which supplies water to Tucson and Phoenix. The upper basin states accused the utility of manipulating the complex system that governs Lake Mead in order to get more water. The Arizona utility denied the charges.