There are a growing number of environment problems associated with human water withdrawals and use. Water scarcity often results in unhealthy aquatic ecosystems because of changes in the timing, quantity, and quality of freshwater flows needed to sustain their natural functions. Data looking at the number of endangered or threatened species of fish, amphibians, gastropods, and freshwater mussels show that aquatic species are exposed to higher extinction risk than other species.vi Major dam construction and water withdrawals on river systems in arid parts of the world, including the Southwestern United States mean that virtually the entire flow of some of these rivers is now captured and used before reaching the rivers’ mouths. This, in turn, desiccates their delta estuaries, shrinks wetlands, cuts off nutrients to the sea, reduces critical habitat for marine fisheries, and brings economic, social, and cultural ruin to coastal human populations.