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R;, The delta's largest remaining wetland is the Cienega de Santa Clara. harder than the MSCP because the potential area for restoration is larger and there are more institutions that could be involved. Osvel Hinojosa is director of conservation in Sonora for Pronatura Noroeste, a Mexican nongov- ernmental entity (NGO) working on delta restoration. Some of the largest patches of riparian habitat remaining in the entire Colorado River basin occur between Morelos Dam and the mouth of the river on the Mexican side of the border, he said. For the riparian corridor to maintain ecological health, it must have base flows of water and periodic, higher pulse flows to promote natural regeneration of cottonwoods and willows, Hinojosa said. "The long -term health of the riparian corridor will depend not only on the base flows but also on a binational solution for pulse flows," he said. Under current operating practices, what is left of the Colorado's historic delta area is sustained by administrative losses, water bypassed to Mexico from U.S. sources, occasional excess flows that can't be used or stored in U.S. reservoirs and any water unused by Mexico (including agricultural return flows). Such excess flows, or pulse flows, occur unpredictably about once or twice a decade, a rate some believe is not frequent enough to sustain the habitat. A part of the Mexican Delta, the Cienega de Santa Clara, has emerged in recent years as a focal point for restora- tion. The 12,000 -acre marsh is the largest remaining wetland in the Colorado River delta region, and is maintained by saline agricultural drainage flows from the Wellton- Mohawk Irrigation and Drainage District across the border in the U.S. Hinojosa describes the Cienega as a very important area for birds, supporting 70 percent of the total population of the Yuma clapper rail, an endangered bird protected by both countries. YDP Collaboration The recent history of the Cienega during a drought period is instructive both for what it says about the behavior of stakeholders and the ability of those stakeholders to come up with collabora- tive solutions. As the drought deepened after 2000, water users and suppliers, notably the Central Arizona Project (CAP), grew anxious that their Colorado River supplies could be cut back, so some called for operation of the YDP as an additional source of supply. The idea was that reducing salinity in the drain water now discharged to the Cienega would qualify it to be sent to Mexico as part of the 1944 treaty obligation, thus freeing up a corresponding amount of Colorado River water for use in the U.S. The 1944 treaty requires the U.S. to deliver 1.5 million acre -feet per year of Colorado River water to Mexico. That idea alarmed environmentalists. They feared operation of the desalter would reduce the average 108,000 acre - feet of water flowing each year from Wellton- Mohawk drains to the Cienega, potentially jeopardizing its marsh habitat. By 2003, positions had hard- ened into what looked like an intractable border water conflict. But in April 2005, an unlikely collaboration of environmentalists, CAP officials and state and federal representa- tives announced agreement on a set of recommendations under which the YDP could be operated and the current bypass flows that sustain the Cienega replaced by water from other sources. Culp, who was part of that YDP/ Cienega work group, said the process could be a model for binational discus- sions to address other border issues. A key to the workgroup's success, Culp said, was that members came to Border issues panelists (14) Chris Frahm (moderator), Bob Snow, Dan Hentschke, Malissa Hathawav McKeith, Peter Culp, Osvel Hinojosa. 6 • COLORADO RIVER PROJECT • RIVER REPORT • WINTER 2005 -2006