CORONADO, Calif. - The United States and Mexico agreed Tuesday to new rules on sharing water from the Colorado River, capping a five-year effort on how to spread the pain of drought and reap the benefits of wet years.
The far-reaching agreement gives Mexico badly needed water storage capacity in Lake Mead, which stretches across Nevada and Arizona.
Mexico will forfeit some of its share of the river during shortages, bringing itself in line with western U.S. states that already have agreed how much they will surrender when waters recede. Mexico also will capture some surpluses when waters rise.
Also under the plan, water agencies in California, Arizona and Nevada will buy water from Mexico, which will use some of the money to upgrade its canals and other infrastructure.
The agreement, coming in the final days of the administration of Mexican President Felipe Calderon, is a major amendment to a 1944 treaty considered sacred by many south of the border. The treaty grants Mexico 1.5 million acre-feet of river water each year - enough to supply about 3 million homes - making it the lifeblood of Tijuana and other cities in northwest Mexico.
The pact represents a major departure from years of hard feelings in Mexico about how the U.S. manages the 1,450-mile river, which runs from the Rocky Mountains to Mexico. In 2001, U.S. states established rules on how to divide surpluses but set aside nothing for Mexico. Several years later, the U.S. government lined a border canal in California with concrete to prevent water from seeping through the dirt into Mexican farms.
"We have chosen collaboration over conflict, we have chosen cooperation and consensus over discord," said U.S. Interior Secretary Ken Salazar, who called the new pact the most important international accord on the Colorado River since the 1944 treaty.
Mexico will begin to surrender some of its Colorado River allotment when the elevation in Lake Mead drops to 1,075 feet and begin to reap surpluses when it rises to 1,145 feet. Mexico will be allowed to store up to 250,000 acre-feet of water in the reservoir and draw on nearly all of those reserves whenever needed.
The agreement expires in five years and is being billed as a trial run, potentially making it more palatable in Mexico.
"These are big political steps for Mexico to take," said Jeffrey Kightlinger, general manager of the Metropolitan Water District of Southern California, which will buy some of Mexico's water. "Chances are we won't have a surplus and we won't have a shortage but, if we do, we'll have the guidelines in place on how we're going to handle it."
In 2007, facing an eight-year drought, California, Arizona and Nevada agreed on how much each state should sacrifice during shortages on the river. That same year, the U.S. and Mexico promised to work on ways to jointly address shortages.
The negotiations gained a sense of urgency for Mexico in 2010 after a magnitude-7.2 earthquake damaged canals and other infrastructure, forcing it to store water temporarily in Lake Mead.
"No matter how sacred the treaty is, and it is, the evidence is overwhelming that you have to adjust it," said Carlos de la Parra, who advised the Mexican government on the agreement.
Los Angeles-based Metropolitan and two other agencies - the Southern Nevada Water Authority and the Central Arizona Water Conservation District - will buy water from Mexico as part of $21 million in payments from the U.S. to Mexico that also call for wetland preservation and other environmental measures south of the border.
California's largely agricultural Imperial Irrigation District, the largest single recipient of Colorado River water, refused to sign the agreement because it felt it should have been allowed to buy some of the water from Mexico. U.S. officials said they hoped to address those concerns.
"This is such a historic arrangement that I think, at the end of the day, it's going to be difficult for Imperial not to sign on," Salazar said.
The river is also a major source of water for Colorado, New Mexico, Utah and Wyoming.
Associated Press writer Ken Ritter in Las Vegas contributed to this report.