About the river

The Colorado River is a vital source of water, hydropower, recreation, ecosystem services, and other amenities for people in the seven basin states (Colorado, Wyoming, Utah, New Mexico, Arizona, Nevada, and California), over two dozen federally recognized tribes, and the Republic of Mexico. Over 40 million people rely on the Colorado River and its tributaries in part or in full for their municipal water supply, while 5.5 million acres of irrigated crops and pasture depend on this water too. Due to rapid growth in southwestern cities and new irrigation projects, overall basin water use increased by over 50% between 1960 and 2000.

The enormous storage capacity of the system’s reservoirs (about 60 million acre-feet), mostly held in Lake Powell and Lake Mead, historically buffered the large variability in the river's flow, allowing for consistent water deliveries to the Lower Basin states (California, Arizona, Nevada), and to many Upper Basin water users as well. But since 2000, the basin has experienced an extended dry period during which the average annual streamflow has been about 20% lower than the long-term average of 15 million acre-feet. While overall basin water use has slightly declined since 2000,

The depleted state of system reservoirs leaves the system vulnerable; the water surface elevation of Lake Mead has hovered around the upper thresholds (1075’ and 1090’) for imposing curtailments on Lower Basin states under the 2007 Interim Guidelines and the 2019 Drought Contingency Plan.

This recent drought, along with the increasing recognition that rising temperatures impact the hydrology of the basin, has led to further concerns about the long-term reliability of basin water supplies. Warming temperatures observed across the basin in the last few decades have discernibly impacted snowpacks, melt and runoff timing, runoff efficiency, and total basin runoff. It is unclear whether the period of below-normal precipitation since 2000 is indicative of future precipitation, but unless average basin precipitation increases substantially, system runoff and water supply are expected to decline over the next several decades due to warming alone.