Colorado River Delta - Natural History

Natural History

Until the early 20th century the Colorado River ran free from its headwaters in the Rocky Mountains of Colorado southwest into Mexico, where it flowed into the Gulf of California. Significant quantities of nourishing silt from throughout the Colorado River Basin were carried downstream, creating the vast 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. Spread across the northernmost end of the Gulf of California, the Colorado River delta’s vast riparian, freshwater, brackish, and tidal wetlands once covered 7,810 km² (1,930,000 acres) and supported a large population of plant, bird, and marine life. Because most of the river’s flow reached the delta at that time, its freshwater, silt, and nutrients helped create and sustain a complex system of estuarial wetlands that provided feeding and nesting grounds for birds, and spawning habitat for fish and marine mammals. In contrast to the surrounding Sonoran Desert, the Colorado River delta’s abundance was striking.