Lake Powell
An aerial view of Lake Powell, where water levels have declined dramatically to lows not seen since it was filled in the 1960s. REUTERS/Caitlin Ochs

One cannot overstate the importance of Colorado River water in the evolution of Southern California from a collection of small cities and villages into a megaregion of 20-plus million people — more than the population of all but three states.

In the early years of the 20th century, Los Angeles imported water from the eastern slope of the Sierra to fuel its growth, but the semi-arid region still needed more and in the 1920s looked to the Colorado River, California’s eastern border with Arizona, which at the time was only lightly tapped.

Imperial Valley farmers had been drawing water from the Colorado for several decades but most of the river’s water, originating in runoff from the Rocky Mountains hundreds of miles away, ran freely into what was then called the Gulf of California.

Southern California created a multi-county Metropolitan Water District, dubbed “the Met.” Its voters passed a bond issue and in 1934 the federal Bureau of Reclamation began work on the Parker Dam, creating Lake Havasu, while the Met began building a 240-mile aqueduct to carry the lake’s water to Los Angeles, San Diego and the region’s other fast-growing cities.

Simply put, without that water, more than a million acre-feet a year, Southern California’s economy and population could not have become as large as they did. Eventually, the region needed more water and the California Aqueduct, carrying water originating as far north as Mount Shasta, became an even more important source.

As Parker Dam was being built to serve Southern California, the federal government was building the much-larger Hoover Dam (creating Lake Mead) and later still another major dam, Glen Canyon (Lake Powell). Other states — particularly Nevada and Arizona — began demanding bigger shares of the river’s water as their own populations boomed.

Over the last several decades, those using shares of the river’s water have squabbled more or less constantly over who gets what, while the Colorado’s flow drifted downward due to drought. Water levels in Lake Mead and Lake Powell have declined to levels that threaten their viability and the federal government has insisted that states bordering the river reduce their diversions.

Multi-state negotiations failed to generate an agreement so on Tuesday, the Bureau of Reclamation, while allowing talks to continue, issued mandatory reductions hitting Arizona hard, with a 21% reduction, imposing much smaller cuts for Nevada and Mexico and, somewhat surprisingly, declaring “no required water savings contribution for California in 2023.”

It was a recognition that the Met was already making serious conservation efforts and, it would appear, the fact that the Imperial Irrigation District has very senior rights to more than 3 million acre-feet of Colorado River water each year.

Tuesday’s action is a milestone of sorts in the history of Colorado River diversions, but certainly not the last word.

It’s possible that the affected states — Arizona particularly — will go to court and if the river’s flows continue to decline, which seems inevitable, there will be continued pressure from the Bureau of Reclamation to reduce diversions even more.

The million-plus acre-feet of Colorado water that Southern California takes each year is still important but the region is not as dependent on it as it once was. Rather, it’s just one aspect of California’s larger water supply crisis.

The Imperial Irrigation District’s much-larger share symbolizes the fact that in California, agriculture is by far the largest consumer of water. Slowly, the state is moving toward reducing farm water to improve wildlife habitat and maintain urban supplies and Imperial’s relatively huge allotment of Colorado water — larger than Arizona’s — could become a major factor in that shift.

CalMatters is a public interest journalism venture committed to explaining how California’s state Capitol works and why it matters.



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Ellen Bullock