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820 NATURAL RESOURCES JOURNAL {Vol. 40 Fall 2000] MANAGING ECOSYSTEM CONSERVATION 821 I. INTRODUCTION that reservoirs filled behind upstream dams and captured floodwaters, almost no freshwatp.I flows reached the Delta. Once Lake ='dfilled behind Glen Canyon Dam in 1981, flood flows began periodically to reach the Delta, and the Delta's ecosystems began to make a slow comeback.' From 1980 to 1998, total water releases to the Delta have amounted to an estimated 20 percent of the Colorado's total flows over the same period, most of it either floodwater or wastewater from agricultural and municipal sources. Despite the irregularity of flood flows and the high salinity and pollutant content of wastewater, these sources of c: water have begun to revive some areas of the Delta. Recent hydrologic and ~ institutional conditions have unintentionally and inadvertently caused ~ wetlands and riparian vegetation to flourish on about 150,000 acres, an " important restoration of habitat. - As long as these conditions prevail, the Delta's existing ecosystems should continue to thrive. Large, established demand for water by irrigators, cities, and other important constituencies makes it extremely unlikely that substantial pre-development-like flows can be restored to the Delta in the short term. Nevertheless, the habitat gains of recent years should be acknowledged and protected, as a run of dry years or additional water consumption upstream along the river could jeopardize existing Delta ecosystems. Even in its present state, the Delta is the largest remaining wetland system in the southwest region of North America and supports a very productive estuary. As ongoing field studies document the ecological, social, and economic values of the Delta's ecosystems, it is increasingly likely that these values will be recognized in deliberations over the allocation of surplus waters, and that instream flows may be dedicated to sustain them.s At the same time, increasing population throughout the region and growing pressures on water, land, and other resources will intensify the strain on the Delta. Water users both north and south of the border may be forced to make difficult choices about Colorado River allocations. Prior to the construction of major dams1 along its route, the Colorado River fed a great delta in the midst of the Sonoran desert. Spread across the northernmost end of the Gulf of California} the Colorado River delta's (Delta) vast riparian, freshwater, brackish, and tidal wetlands once covered 1,930,000 acres (475 square miles) and supported a wealth of plant, bird, and marine life. As most of the river's flow reached the Delta, freshwater, silt, and nutrients helped create a complex system of wetlands that provided feeding and nesting grounds for birds, and spawning habitat for fish and crustaceans.3 The legendary richness of the Gulf of California can be attributed to the Delta's productivity as well as its capacity to support marine and bird life. In contrast to the aridity of the surrounding Sonoran Desert, the Colorado River delta's abundance was striking. In A Sand County Almanac, Aldo Leopold recalled a visit: I have never gone back to the Delta of the Colorado since my brother and I explored it, by canoe, in 1922... .For all we could tell, the Delta had lain forgotten since Hernando de Alarc6n landed here in 1540....On the map the Delta was bisected by the river, but in fact the river was nowhere and everywhere, for we could not decide which of a hundred green la~oons offered the most pleasant and speedy path to the Gulf. Today, conditions in the Delta have changed. Like other desert river deltas, such as the NileS and the Indus,' human activity has greatly altered the Colorado River delta. Decades of dam construction and water diversions in the United States and Mexico have reduced the Delta to a remnant system of small wetlands and brackish mudflats. During the years 1. There are more than 20 storage reservoirs with capacities greater than 20,000 aae-feet in the Colorado River basin (an aae-foot is 325,851 gallons of water, roughly the amount two families of four use in one year). Total storage capacity in these reservoirs exceeds 60 million a~feet, four times the river's average annual flow. The two largest reservoirs in the basin are Lake Mead (25.88 million aae-feet) and Lake Powell (24.32 million aae-feet). See DALE PON1lUS, SWCA, INc., COLORADO RIVER BASIN STuDy: REPoRT TO mE WESTERNW ATER POllCY REvIEw ADVISORY COMMISSION 9 (1997). 2. The Gulf of California is also known as the Sea of Cortez. 3. See Edward P. Glenn et al., F.ffects of Water Management on the Wetlands of the Colorado River Delta, Mexico, 10 CONSERV AnON BIOLOGY 1115, 1116 (1996). 4. ALDO LBoPOLD, A SAND COUNTY ALMANAC 141-42 (1968). 5. See generally Daniel Jean Stanley ok Andrew G. Warne, Nile Delta: Recent GeologiCRI Evolution and Human Impact, 260 ScIBNCB 628 (1993). 6. See generally Robin M. Leichenko ok James L Wescoat Jr., Environmental Impacts of Climatic ChAnge and Water Development in the Indus Delta Region, 9 WATER REsoURCE DEV. 241 (1993). 1. For the purposes of this article, a flood. is any volume of Colorado River water that aosses the U.S.-Mexico international border and is delivered at a rate that exceeds Mexico's diversion capacity and inundates land (either within the levees or beyond) that is nol'DUllly dry. These floods occur as a result of releases from U.S. reservoirs for flOQCi control pwposes (or other reasons). or directly as a result of flooding in the United States (e.g., flooding in the Gila basin). 8. Department of Interior 5eaetary Bruce Babbitt noted. that there should be "no net loss to environmental resources'" In the Colorado River delta, in extemporaneous remarks dwing his 1999 speech to the Colorado River Water Users Association. Department of the Interior 5eaetary Bruce Babbitt, Remarb at the Meeting of the Colorado R.iver Water Users Association Annual Meeting (Dec:. 11. 1999) (tape available at the Colorad.o River Water Users Association. Coac:hella, CA).