Federal government plan outlines cuts of roughly 40% to California, Arizona and Nevada but fix is likely to be only temporary

The US government released its anxiously awaited plan for how to manage the Colorado River crisis on Friday, which includes the potential for harsh cuts in water supplied to California, Arizona and Nevada.

Under the proposal, the so-called lower basin states stand to lose up to 3m acre-feet (3.7bn kiloliters) a year – enough water annually to serve more than 25 million people and roughly 40% of their collective total. The so-called upper basin states – Colorado, Utah, New Mexico and Wyoming – were spared from mandates restricting their supply.

The Colorado River supplies roughly 40 million people in seven states, two countries and dozens of tribes, and also irrigates 5.5m acres (2.2 hectares) of farmland. The federal government has limited jurisdiction over state-based water policy but is responsible for managing the dams at Lake Powell and Lake Mead, the two key reservoirs that lower basin supplies flow through.