Lake Mead quarter full as US imposes Colorado River cuts

Lake Mead, America's largest reservoir, is now about a quarter full as drought, heat and overuse strain the Colorado River system that supplies water to more than 40 million people across seven states.

A pale mineral “bathtub ring” around the reservoir near Las Vegas now sits 186 feet, or 57 meters, above the water surface, showing how far the lake has fallen over a quarter century of drought.

The Colorado River feeds a vast water system serving cities including Las Vegas, Los Angeles and Phoenix. Lake Mead and Lake Powell store snowmelt-fed water for year-round distribution, and their dams generate electricity for hundreds of thousands of households.

David Kreamer, a hydrology professor at the University of Las Vegas, said an abnormally dry winter reduced Rocky Mountain snowpack, while the hottest July ever recorded in the United States increased evaporation from Lake Mead.

Lake Powell hit an all-time low in August. Both reservoirs are close to the level at which electricity generation would be affected. A further drop could produce “deadpool” conditions, where water no longer flows through the dams.

Kreamer said disruption to Colorado River irrigation could affect food supplies beyond the river basin because many winter vegetables in the United States are grown in California.

The Trump administration this month published a 10-year plan imposing large restrictions on the water California, Arizona and Nevada can use. The three lower-basin states must cut their take by a total of 3.7 billion cubic meters a year, while Colorado, Utah, Wyoming and New Mexico were spared.

Nevada filed a lawsuit on Monday over the imbalance. The dispute comes as western states argue over how to divide a river whose 1922 interstate treaty allocated more water each year than the river can provide.