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This study reviews the challenges of managing the scarce water resources of Mexico's El Pinacate and Gran Desierto de Altar federal reserve in northwestern Sonora, Mexico. El Pinacate is a unique natural area and habitat to a number of plant and animal species, including the endangered Desert Pupfish. The El Pinacate-Gran Desierto de Altar reserve was established in 1993 with the joint purpose of preserving this extraordinary ecosystem while taking into account the sustainable development needs of those communities located within the reserve's confines. A defining feature of the El Pinacate-Gran Desierto de Altar reserve is the lack of perennial water sources. A portion of the Rio Sonoyta is the only reliable year round water source within the reserve and is supplemented by naturally occurring rock tanks and catchments that are replenished by occasional rains and may contain water year-round depending oil precipitation patterns. These few permanent water sources have historically determined the pattern of human settlement and remain vital for the small communities located in or near the reserve. Ranching and mono-crop agriculture are the principal sources of human livelihood.

Water use on the Rio Sonoyta has binational implications. Yet, despite the existence of an international groundwater agreement between Mexico and the United States, no specific agreement has been struck on groundwater conservation for the Rio Sonoyta. Intensive water uses in the region can be dated to the introduction of wells on the Rio Sonoyta in 1952. Groundwater development was encouraged by the Mexican government in order to develop farming and ranching opportunities in the area. By 1983, as many as 290 wells were recorded in the region with a total pumping capacity of 23,203 gpm. The number of wells in use subsequently declined, totaling 120 in 1993. Since the reserve's establishment, the government has placed a moratorium on new well development, but documented annual withdrawals are still 2.5 times the annual recharge rate. Upstream water development on the Rio Sonoyta beyond the reserve perimeter has diminished well-water supplies of small in-reserve settlements, provoking downstream diversions that adversely affect rare aquatic species such as the Desert Pupfish. Declining wafer stocks may also affect other animal species, but this has yet to be scientifically demonstrated.

As the problems of water development on the Rio Sonoyta affect the El Pinacate-Gran Desierto de Altar reserve they fake on all international dimension. The Rio Sonoyta crosses the boundary and is utilized by both countries. There is, thus, an urgent need for a binational agreement that would help conserve the river's wafer resources for the sustainable development of human communities and the preservation oft he region's fauna and flora. Unfortunately, current binational initiatives, such as the Border XXI Program, while advancing the goal of sustainable development of borderland natural resources, fail to identify the Rio Sonoyta as one of the transboundary rivers and st reams warranting binational attention. The conservation of the Reserve's water resources call be accomplished, however, if the provisions of the Reserve Decree of 1993, recent revisions to the National Water Law, and the objectives of the Border XXI Program are taken into account. Additional measures should be taken, however, including clarifying the water rights and responsibilities of current users, regularizing the water supply within the reserve as provided for in the National Water Law, developing monitoring and management plans for the various water sources within the Reserve, developing and implementing public education programs on water conservation within the region, developing a joint management plan between El Pinacate and Organ Pipe National Monument in Arizona, and, ultimately, realizing a ground water treaty between the two countries that has the aim of conserving and managing the Rio Sonoyta's water resources.