The White House has announced a key deal with Arizona, California and Nevada to conserve large amounts of water from the drought-afflicted Colorado River.

The breakthrough agreement aims to keep the river, which has been shrinking at an alarming rate due to climate change and overuse, from falling to a level that could endanger the water and power supply for major cities in the West and vast stretches of hugely productive farmland.

Water managers in Arizona, California and Nevada have agreed on a plan to cut their water use by well over a third of the entire traditional flow of the Colorado River through the seven states that rely on it. The federal government will pay some $1.2 billion dollars to cities, irrigation districts and Native American tribes if they temporarily use less water.

The deal, which only runs through the end of 2026, amounts to the largest reductions of water use in modern times and are very likely to require significant water restrictions for farms and residents across the Southwest.

Much of this conservation deal is happening though thanks to a big infusion of federal funds into the region that will do things like pay farmers to fallow some of their land. The government is also compensating water districts and tribes to voluntarily keep some of their legally entitled water in the nation's largest reservoir, Lake Mead, in order to prevent it from going dry.

Kathryn Sorensen, research director at the Kyle Center for Water Policy at Arizona State University, says another big reason the deal came together at the last minute is due to the fact that much of the West saw record snow last winter.

"The good snowpack bought us the luxury of bringing forward a deal that wasn't quite as much as the federal government was hoping for but it does buy us time," Sorensen says.

Experts expect further and much deeper cuts than announced Monday will be necessary after 2026.

The cuts in the deal are entirely voluntary. But it does avert - for now - the federal government coming in and announcing across the board water cuts across Arizona, Nevada and California.

"That's important because the minute the federal government does that, someone's going to sue," Sorensen says.

This conservation deal first announced by the White House comes as California for months had refused to agree to a brokered deal with the other states, as large users in the state tend to hold senior water rights on the river.