Colorado and five other Colorado River states have reached a consensus on how they plan to reduce their water usage, the states announced Monday.

California, notably, is not a part of the consensus.

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The proposal, which the states will submit to the federal Bureau of Reclamation, suggests changes to the criteria for Colorado River usage reductions, including operating guidelines for Glen Canyon Dam at Lake Powell and Hoover Dam at Lake Mead.

The states had until Tuesday to establish major cutbacks in water use.

The proposal is being submitted at a time when federal pressures to reduce water use are high and the river system nears catastrophe, with lakes Mead and Powell approaching critical levels. The Colorado River has been listed as the most endangered river in the U.S., according to a report from the nonprofit organization American Rivers.

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The proposal was signed by Colorado, Arizona, Nevada, New Mexico, Utah and Wyoming — but not California, drawing criticism from U.S. Sen. Michael Bennet, D-Colo., who called the state's decision "deeply disappointing."

"We are facing the most serious drought in 1,200 years," Bennet said in a statement. "California must step forward and be part of the solution. For too long, the other six states, and particularly the Upper Basin, have carried the burden of this historic drought."

The Colorado River supplies water to 40 million people in two countries, seven states, 29 federally recognized Indian tribes, and 4 million acres of farmland. But its ability to provide that water faces a serious challenge following 22 years of drought and a drier climate that reduced its annual flow from 16.4 million acre-feet (MAF) to around 14.5 MAF on average since 2000.

Colorado River states faces new deadline on water usage reductions

Compacts and agreements among the states govern how water from the river is allocated. The 2007 interim guidelines, for example, set up a series of tiers for when water levels at Lake Mead drop to critical low levels. Those tiers would dictate cuts in water allocations to the lower basin states.

In 2019, another round of agreements, known as the Drought Contingency Plan, dictated just how water would be cut from the lower basin states should the shortages at Mead reach those levels.

California, for now, has so far been spared cuts under the 2007 interim guidelines and the 2019 drought plan, but under a Tier 3 shortage, the state would take less water from the guideline's Intentionally Created Surplus (ICS) Program, which creates water credits in Mead through conservation measures and which could be reclaimed at some point in the future.

California is also part of a lower basin plan, known as 500+, signed last December, that would keep about a million acre-feet of water in Mead for the next two years through conservation measures and at a cost of $200 million, split between the states and the federal government.

The interim guidelines are in effect until Dec. 31, 2025 and are now the subject of negotiations among the upper and lower basin states.

The proposal by the six states calls for reduced releases from lakes Powell and Mead, and additional combined reductions of 250,000 acre-feet and 200,000 acre-feet at two Lake Mead elevations to Arizona, California and Nevada.

The federal government is expected to evaluate and incorporate the proposal into a Supplemental Environmental Impact Statement to update operation guidelines originally established in 2007. 

The river originates high in Colorado’s Rocky Mountain National Park and collects water from major tributaries that then flows through a seven-state river system. The basin is split into two regions: The Upper Basin includes Colorado, Wyoming, New Mexico and Utah; the Lower Basin includes Arizona, Nevada and California.

“We recognize that over the past twenty-plus years there is simply far less water flowing into the Colorado River system than the amount that leaves it, and that we have effectively run out of storage to deplete,” the states say in their proposal, pledging continued collaboration with the federal government, water users, Basin tribes and others.

Last year, when the river was confirmed to be at its driest period in 1,200 years, the federal government asked the seven river states to reduce water use by 2 million to 4 million acre-feet. The discussions were hindered by competing priorities and disagreements over the role each state should take in reduction efforts and a consensus was not met. 

“I am encouraged today that six states came to an agreement on potential mechanisms to better manage the critical reservoirs on the Colorado River,” Colorado Gov. Jared Polis wrote in a statement. “Increased drought, climate change, and overuse has led to less water in our reservoirs. More must be done to protect the system, and although we did not cause this crisis, I am proud that Colorado is part of the solution.”

“We forged a common vision that will protect the Colorado River and the 40 million people, and more than 30 Tribes, who rely on it,” Bennet said.