Colorado River Delta. Prior to the construction of major dams along its route, the Colorado River fed one of the largest desert estuaries in the world it once covered 7,810 km2. The loss of freshwater flows to the delta over the twentieth century has reduced delta wetlands to about 5 percent of their original extent.. Baja California, Mexico..© March 5 2008 Marco van Middelkoop/Aerophoto-Schiphol.