Mexico receives a precise allocation of 1.5 million acre-feet of Colorado River water each year under a binding 1944 treaty, World Atlas reported, but upstream consumption and severe drought leave the channel entirely dry long before it reaches the Gulf of California.
The 1944 Treaty and Mexico’s Fixed Allocation
The 1944 bilateral treaty between the United States and Mexico established a firm, legally binding guarantee that has endured for 80 years. While the 1922 Colorado River Compact carved up 15 million acre-feet between U.S. states—assigning 7.5 million acre-feet apiece to the Upper Basin states of Colorado, New Mexico, Utah, and Wyoming and the Lower Basin states of Arizona, California, and Nevada—Mexico’s share was added two decades later.
That 1.5 million acre-feet amounts to just under 10 percent of the river’s historical flow. As the southernmost entity in the watershed, Mexico holds the smallest portion of the system’s distributed water, requiring rigorous management of every drop.
How the Mexicali Valley Consumes the Supply
Mexico’s entire allotment is captured almost immediately after crossing the border. Situated roughly a mile south of the international boundary is Morelos Dam, the final dam on the Colorado River.
Under standard operating conditions, Morelos Dam diverts virtually all the remaining water into the Reforma Canal. This infrastructure feeds the agricultural fields of the Mexicali Valley, where 1.2 to 1.3 million acre-feet irrigate approximately half a million acres of crops. The remainder of the water supports urban centers like Tijuana and Mexicali.
A Dry Delta and the Impact of Drought Reductions
Because nearly every drop is diverted at Morelos Dam, the river channel below the barrier runs dry for roughly 90 miles before reaching the Gulf of California. Since the 1960s, intensive storage and consumption have drained the river before it meets the sea, transforming the once-vibrant delta wetlands into cracked mudflats.
Exceptions to this dry spell have occurred through binational agreements. Under a 2014 accord known as Minute 319, the U.S. and Mexico opened the gates at Morelos Dam to deliver a 105,000 acre-foot pulse flow downstream, temporarily reconnecting the river to the sea and reviving wildlife habitats for several weeks.
However, Mexico’s water security remains vulnerable to basin-wide shortages. Under operating agreements like Minute 323, which is scheduled to expire in 2026, Mexico shares the burden of upstream deficits. When Lake Mead drops to critical thresholds, Mexico’s delivery is reduced proportionally, forcing a 5 percent cut during the 2022 restrictions as both nations negotiate management terms for an increasingly overdrawn watershed.
