Sustainable water management of river basins requires coordination of federal and state actions. Dams and reservoirs needed to supply water, control flooding or regulate flows are often constructed by the Army Corps of Engineers or the Bureau of Reclamation and operated in accordance with the project purposes specified by Congress. States likewise operate water control and storage structures, and have primary responsibility for managing groundwater and allocating private rights to utilize water. Particularly during droughts, complex problems may arise when scarce surface water or groundwater is shared by states with conflicting views on how water should be allocated and used.