Colorado River Compact: How Water Rights Shaped Arizona’s Development

Few rivers in the world have influenced the destiny of a region as profoundly as the Colorado River. Flowing for over 1,400 miles from the Rocky Mountains to the Gulf of California, it slices through deep canyons, irrigates farmland, and sustains cities across the American Southwest. But behind its lifegiving current lies a document that has governed its distribution for over a century: the Colorado River Compact of 1922.

This pivotal agreement not only carved up water among seven states—it helped shape Arizona’s population growth, agricultural expansion, and political identity.

A River Divided

By the early 20th century, the growing populations of the southwestern United States were already placing heavy demands on the Colorado River. Farmers in California's Imperial Valley relied on its waters, while cities like Los Angeles and Phoenix saw the river as essential to their future.

To avoid future conflicts over access, the federal government—through then-Secretary of Commerce Herbert Hoover—brought representatives from seven basin states together: Arizona, California, Colorado, Nevada, New Mexico, Utah, and Wyoming. In 1922, they signed the Colorado River Compact, dividing the river into Upper Basin and Lower Basin regions, with each allocated 7.5 million acre-feet of water per year.

Arizona, part of the Lower Basin, initially refused to ratify the compact, fearing that California would gain too much control. It wasn’t until 1944, after decades of legal disputes and political resistance, that Arizona formally joined the agreement.

Water as Power, Power as Progress

The Compact set the stage for monumental engineering projects, including the construction of Hoover Dam (1936) and later Glen Canyon Dam (1966). These massive structures helped regulate the river’s flow, generate hydroelectricity, and store water in artificial lakes like Lake Mead and Lake Powell.

Arizona’s eventual inclusion in the Compact cleared the path for its own ambitious project: the Central Arizona Project (CAP). Completed in 1993, the CAP aqueduct carries water from the Colorado River over 300 miles inland to supply Phoenix, Tucson, and agricultural zones in between.

Without the Compact and the infrastructure that followed, Arizona’s explosive growth in the 20th century—especially in its urban corridors—would not have been possible.

An Agreement Under Strain

Though revolutionary for its time, the Colorado River Compact is now a source of contention and concern. The allocations were based on overly optimistic estimates of river flow, and today, the river routinely fails to meet demand, especially during prolonged drought.

As the climate warms and snowpack declines in the Rockies, water levels in Lake Mead and Lake Powell have reached record lows. Arizona, like other Compact states, faces mandatory cutbacks, affecting cities, tribes, and farmers alike.

New negotiations are underway to modernize the Compact.