For decades Mexico and the seven U.S. states within the Colorado River's watershed - Arizona, California, Colorado, Nevada, New Mexico, Utah, and Wyoming - have bickered over how much water must be allowed to flow south past the international border near Yuma, Ariz, and a 1944 treaty requires that 1,500 acre feet of flow per year flow to Mexico.
During many years the amount of that flow that reaches the river's delta has amounted, at most, to brine. The U.S. has had no treaty obligation to deliver water to Mexico for purposes of sustaining the river delta and, as a result, the river's water ceases flowing about 60 miles short of the delta. Over time, this shortage of replenishing flows has caused the delta to substantially shrunk from its historic two million-acre size.
The deal, which was finalized Tuesday in San Diego, will make restoration of the delta environment an authorized purpose of water deliveries across the international border. It commits the U.S., Mexico, and a coalition of environmental groups to annual deliveries of 5,000 acre feet each to the delta.
It will also provide the seven states within the river's drainage basin with more supply certainty during times of drought. Mexico agreed to share surpluses and shortages of water with the U.S. states, a historic change from the terms of allocation that has governed the river for the last 68 years.
During years in which drought conditions prevail in the portion of the river's watershed in the United States, Mexico will forego delivery of some of the water to which it would otherwise be entitled. By contrast, during surplus years, Mexico will be able to store water in Lake Mead.
The U.S. government will also help Mexico finance repairs and improvements to its water delivery system.
Formally known as Minute 319 to the 1944 treaty between the two nations, the agreement will run through 2017. It takes effect immediately.
Map of Colorado River basin courtesy Wikimedia.
