California, Arizona, Nevada and other Western states face a potential water and power-generating catastrophe because the Colorado River they depend on is shrinking. As water levels drop because of overuse and over two decades of drought made worse by climate change, the Biden administration is getting ready to reduce water supplies to states for the first time.

The river is a critical resource. Seven U.S. states with 40 million people —Arizona, California, Colorado, Nevada, New Mexico, Utah, and Wyoming — depend on it for drinking water, agricultural irrigation, hydropower, recreation, fish and wildlife habitat, and other benefits. It also serves two Mexican states. Electricity generated by the Glen Canyon and Hoover dams on two main reservoirs, Lake Mead and Lake Powell, powers millions of U.S. homes and businesses. But both lakes' levels are so low that the federal government will reduce outflow to assure there's enough water to turn turbines that generate electricity and to assure it stays above the valves that let water leave the reservoirs for Arizona, Nevada and California.

The Interior Department, which manages the long river, this spring released a draft plan with two choices of action to protect what it calls "water security:" make cuts based on the longest-held water rights or distribute them evenly across Arizona, California and Nevada by going beyond what each state proposes. The first option would mostly spare California, the Colorado River's largest and oldest user. But that would greatly harm Nevada and force disastrous reductions on Arizona. Public comments on the choices are accepted until May 30. A final analysis, expected this summer, could include other approaches. "Failure is not an option," says Deputy Interior Secretary Tommy Beaudreau.

The federal government can force cuts only on the three states getting water from Lake Mead and Lake Powell. (Four other states draw directly from the river passing through them.) This marks a painful new phase in America's response to the long Western drought. Until now, the federal government has focused on conservation subsidies — paying farmers, cities and Native tribes to voluntarily cut water use. "There's no way to solve this problem on the Colorado River without causing some pain for some people and probably pain for a lot of people," says professor Mark Squillace of the University of Colorado, a specialist in natural resource law.

Expert says: "It will now be up to the states to say, well, we have a better idea — and here it is." — Sharon Megdal, director of the University of Arizona’s Water Resources Research Center

Ex-Cabinet member says: "The impending crisis demands that Interior Secretary Deb Haaland use all powers at her disposal to force the parties to make their fair share of cuts." – Bruce Babbitt, past Arizona governor and federal Interior secretary

Professor says: "The threat of the federal government to impose a solution may light a fire under the states to come up with their own agreement, but it is unlikely they will worry much about Mexico's share of the water." – Heather Cox Richardsdon, Boston College historian