In my plan to manipulate the waterways of New Orleans, I found an unexpected side benefit. The Gulf of Mexico has a large "dead zone," in which an algae bloom has rendered the water oxygenless, and unable to sustain life. This condition can be reversed by ending the flow of farm runoff, as was discovered when the Black Sea near Russia had a dead zone. (That dead zone reversed itself when the Russian region collapsed economically, which meant no more fertilizer use.)
So if I divert the Mississippi as in my plan, the Gulf of Mexico's dead zone would reverse itself within 20 years.