In just a year, the Mississippi went from abnormally high levels to historic lows. That's causing problems.
These images show a stretch of the Mississippi River just south of Memphis, Tennessee. The top one was taken by a NASA satellite on August 8, 2012, and the bottom one by a different NASA satellite on August 14, 2011. See how there are huge patches of light tan along the river in the image from 2012? Those are newly exposed sand bars, the result of record low water levels.