The effects on the delta ecosystem have been profound. Willow and cottonwood forests that used to thrive along the Colorado’s banks and in its wetlands now struggle to survive, while a drought-adapted invasive shrub called salt cedar (tamarisk) dominates. Populations of birds and other animals have dwindled. According to ecologists, only 10 percent of the Colorado’s original wetlands remain, with just 3 percent of cottonwood and willow forests surviving.