The Colorado River Delta is where the Colorado River used to flow into the Gulf of California (Sea of Cortez). This vast, wildlife-rich area was once North Americas largest wetland. Paddling the delta in 1922, naturalist Aldo Leopold was entranced by the flourishing world beyond the tip of his canoe. Verdant walls of mesquite and willow . . . a hundred green lagoons, he wrote. The river was everywhere and nowhere. The use of water upstream in the U.S. and the reduction of freshwater flow has resulted in the loss of most the wetlands of the area.