Wracked by the worst (and longest) droughts in memory, the Midwest and the river are critically short on water, so short that the shallowest stretch of the river between Cairo, Ill. and St. Louis could become unnavigable in the next month, and the Corps of Engineers is just about out of geoengineering options to mitigate the problem

There is one other option. The Corps could open up the controls along the Missouri River--the Mississippi’s biggest tributary--and let its waters flow into the Mississippi. But the Missouri basin itself is already quite parched, and besides it’s illegal for the Corps to do so under its charter. It would likely take an emergency act by the President or Congress to open Missouri River waters up to the Mississippi, and then the Corps would have a whole new problem: a dried up Missouri River and a lot of angry interests along its banks.

So the Corps of Engineers has to go on digging, dredging, and ultimately praying for rain--a reminder that our attempts a geoengineering have a come a long way, but that they currently can take us only so far.