The Mexican Delta is located at the natural terminus of the Colorado River at the Gulf of Mexico, just south of the U.S.-Mexico border. The desert ecosystem was formed by silt flushed downstream from the Colorado and fresh and brackish water mixing at the Gulf.

The Mexican Delta once covered 9,650 square miles but has shrunk to less than 1 percent of its original size due to man-made water diversions.

Even so, the delta still provides important habitat. The desert estuary’s mix of fresh and tidal waters supports a diverse population of birds and animals, including the endangered Yuma clapper rail and the desert pupfish. It also is an important stopover along the Pacific Flyway, a major north-south migratory route for countless numbers of birds.

Colorado River and Mexican Delta Water Supply

The Mexican Water Treaty of 1944 committed the U.S. to deliver 1.5 million acre-feet of water to Mexico on an annual basis, plus an additional 200,000 acre-feet under surplus conditions. The treaty is overseen by the International Boundary and Water Commission. [See also Mexico and Colorado River Water.]

Colorado River water is delivered to Mexico at Morelos Dam, located 1.1 miles downstream from where the California-Baja California land boundary intersects the river between the town of Los Algodones in northwestern Mexico and Yuma County, Arizona.

In 2012, providing water for the Mexican Delta was one of the key components of Minute 319.As part of the five-year restoration pilot program, the U.S., Mexico and non-governmental organizations agreed to jointly provide a total of 52,696 acre-feet of water as base flows to keep water in the channels and Delta year-round for riparian vegetation. The Sonoran Institute, Pronatura Noroeste, and Environmental Defense Fund are required to secure one-third of the total flow that will be allocated to the Colorado River in Mexico, while Mexico and the U.S. will contribute the remaining two-thirds of the flows.