The Colorado River Delta: Progress from 1944

The Colorado River provides water to meet the needs of nearly 40 million people across seven US states and part of Mexico. Historically, the Colorado River ran 1,450 miles from the Rocky Mountains down to the Gulf of California in Mexico. However, within the last century the river has begun drying up just short of its Mexican delta. Before this change, the delta was a vast and diverse ecosystem that sustained over 300 species of birds, and provided lush spawning grounds for many species of fish. Today, the delta looks more like a desert.

The change came in 1944 when the US and Mexico signed a treaty titled “Utilization of Waters of the Colorado and Tijuana Rivers and of the Rio Grande.” The treaty allocated 90% of the Colorado River’s water to the US, and limited the amount of water the US was obligated to pass on to Mexico to 1.5 million acre-feet per year, not to exceed 1.7 million acre-feet per year.

This treaty allowed US citizens to use the Colorado River to establish large cities in otherwise desert climates by extracting drinking and irrigation water. Vast consumption of the river’s water slowly reduced the availability of water in Mexico for the same purposes. Eventually, the two countries grew to consume enough water from the river to keep it from reaching its natural termination.

Minute 319

On November 20, 2012, the US and Mexico signed “Minute 319,” an amendment to the 1944 treaty designed to address multiple issues on an experimental basis over the next five years.  Minute 319 established a method by which the US and Mexico will share in the benefits of high water flow and the burdens of drought in the Colorado River. Mexico gained the right to defer some of its water delivery during times of surplus by temporarily storing water in Lake Mead. In proportion to Lake Mead’s water level, Mexico may then order the previously deferred water, up to 200,000 acre-feet per year, to make up for reductions in base flow during droughts. Reductions in base flow due to drought are also determined in proportion to Lake Mead’s water level, and return of Mexico’s stored water will be refused when the water level of Lake Mead is below 1,075 feet. These provisions will help increase water use efficiency and the reliability of Lake Mead’s water level.

Also outlined in Minute 319 is a pilot program addressing the issue of ecological restoration in the Colorado River delta. For the program, the US agreed to give Mexico $21 million to be used for construction on Mexican water infrastructure to improve efficiency, to develop programs to enrich the ecology of the delta, and to fund half of the supply of a new pulse flow and base flow in the river. As consideration for the $21 million, Mexico agreed to transfer ownership of 124,000 acre-feet of its deferred water to the US before 2018. The pulse and additional base flow are aimed at increasing water delivery to the delta by 2014. The pulse flow will consist of a single delivery of roughly 100,000 acre-feet of water, followed by 50,000 acre-feet per year of additional base flow. A report about the effects of the additional flows on the delta will be published by 2018. Both governments hope to see hydrological and biological restoration in the delta as a consequence of this pilot program.

Finally, Minute 319 implemented a 50-acre environmental restoration project just south of the US-Mexico border on the Colorado River. Several other proposed projects in environmental restoration, water conservation, and establishing new water sources were listed as potential future endeavors.


Though many view Minute 319 favorably—as headway for fairness in water use and environmental protection—some groups have spoken out against the agreement. Mexico’s National Farmer’s Confederation has united in opposing Minute 319, arguing that the transfer of 124,000 acre-feet of water for $21 million is not in their interest. The organization claims that farmers along the Colorado River in Mexico will not be able to meet the water needs of their crops as a result of the reduction in available water.

Additionally, the California-based Imperial Irrigation District (“IID”), the organization with the largest allotment of Colorado River water in the US, has raised some concern about the distribution of the 124,000 acre-feet of water that will be transferred to the US from Mexico. Currently, the additional water is to be split among Arizona, Nevada, and California, with the entire Californian share going to the California Metropolitan Water District (“CMWD”). IID argues that the CMWD does not have a right to the entire Californian share, and that the water should be split between them. Negotiations over allotment of the extra water have not taken place between the two organizations. IID has expressed interest in the past about storing its own water in Lake Mead to help meet water needs, but it has never been allowed to do so. In light of the additional water to be stored in Lake Mead by Mexico, IID and others have also expressed some concern about decreased production of hydroelectric power and less reliable indication of drought conditions based on Lake Mead’s water level.


There are still details that need to be worked out in implementation, but the overall message of Minute 319 is that the US and Mexico are working together towards restoring the hydrology and biology of the Colorado River Delta. The desert-like landscape that once was a lush and vibrant ecosystem may one day return to something resembling its natural state. Minute 319 is but the first step towards significant environmental restoration