Well, to be perfectly honest, well-engineered projects manage rivers in the US as well - e.g. the system of locks and dams all along the Mississippi courtesy of

Well, to be perfectly honest, well-engineered projects manage rivers in the US as well - e.g. the system of locks and dams all along the Mississippi courtesy of the US Army Corps of Engineers. The two big problems with the management of the Colorado River water are big disincentives not to lose legal water rights, resulting in farmers growing water-hungry crops in the desert just to preserve those rights; and water allocations that were larger than even optimistic Colorado River flow rates during a very wet season in the 1930s. In order to preserve the river basin and reservoirs, both of those issues have to be addressed, concurrently, and there are a lot of stakeholders that are going to be very angry about whatever solution is proposed to them (or imposed on them very soon, out of necessity, to keep the lights on.)