What was once a marina sits high and dry due to Lake Mead receding in the Lake Mead National Recreation Area in Arizona, July 16, 2014.

John Locher/AP

Arizona delivered one of the final puzzle pieces for a Colorado River drought plan, agreeing Thursday to join six other states and Mexico in voluntarily taking less water from the constrained river.

The decision to join the drought plan, authorized by lawmakers and Gov. Doug Ducey, went right up to the edge of a federal deadline that threatened to blow up the agreement. U.S. Bureau of Reclamation director Brenda Burman said all parties must agree to cutbacks by Jan. 31 or she would begin the process to impose them.

Arizona was the only state that required legislation to join the agreement to protect the water that serves 40 million people in Wyoming, Colorado, Utah, New Mexico, Arizona, Nevada and California.

“We inherited as human beings a pristine land with pristine water, and we messed it up as human beings ourselves,” said Sen. Jamescita Peshlakai, a Democrat who represents the Navajo reservation in northeastern Arizona and voted to join the drought plan. “It is incumbent for us to safeguard, protect what we have left.”

The so-called drought contingency plan is an effort to keep the Colorado River’s major reservoirs from reaching catastrophically low levels.

The nightmare scenario for Arizona, California, Nevada and Mexico — which draw from Lake Mead — is a phenomenon called “dead pool,” in which the level of the lake’s surface falls below the gates that let water out. To avoid it, the agreement calls for an escalating array of cutbacks as the lake level drops.

Arizona has junior rights to river water and would be hit first and hardest if Lake Mead on its border with Nevada drops to shortage levels. Most residents will not see an impact from cutbacks, which will primarily hit farmers in Pinal County — between Phoenix and Tucson — who have the lowest-priority access to Colorado River water and stand to lose the most.

The Arizona legislation is the product of months of negotiations between major water users in the state, who agreed to reduce their take in exchange for cash or access to groundwater in the future. The farmers, who reluctantly supported the agreement, said it would require them to fallow as much as 40 percent of the county’s farmland.

“We know nothing is perfect, but this is pretty darn good,” said Senate President Karen Fann, a Republican from Prescott.

Arizona water officials say joining the agreement is critical to the state’s water future.

“The drought is real, and there’s less water in the river,” Dennis Patch, chairman of the Colorado River Indian Tribes, told lawmakers this week. “We can see it. We must all take a realistic view of this river and realize it does not have as much water as it used to.”

Opposition came from a handful of Democrats who said the deal didn’t do enough to rein in the state’s water consumption. Sen. Juan Mendez characterized the deal as a giveaway to interest groups that promotes unsustainable water policy, ignores climate change and doesn’t address the fact that Arizona will have less water in the future.

If Arizona were serious about the drought, Mendez said, “we would be entertaining an honest assessment of whether we can continue to base our state’s economy on continuous growth and on welfare for water intensive uses.” Mendez, a Tempe Democrat, was one of only a handful of lawmakers to vote against the measures.

Arizona lawmakers backed two measures. One allows Arizona to join the multi-state agreement. The other includes a variety of measures to help Pinal County farmers. Those include $9 million for the farmers to drill wells, dig ditches and build other infrastructure needed for them to change from the river to groundwater.

Tucson would get more groundwater credits for treated wastewater, allowing the city to pump more in the future in exchange for providing water to Pinal farmers.

The drought plan requires Arizona to find a way to reduce its use of Colorado River water by up to 700,000 acre-feet — more than twice Nevada’s yearly allocation under the drought plan. An acre-foot is enough for one to two households a year.

Still, the agreement is only the beginning of discussions about conserving Colorado River water. It lasts through 2026, after which point even steeper cuts are widely expected. Ducey created a commission Thursday to study ways the state can conserve water.

“There’s a lot more work to be done to ensure that Arizona is prepared for a drier water future,” Ducey said.