The Mississippi is surrounded by a vast network of concealed plumbing that underlies the whole of the American Midwest. As for the great river at the heart of this maze, it is now for all intents and purposes a man-made artifact. Every inch of its course from its headwaters to its delta is regulated by synthetic means—by locks and dams and artificial lakes, revetments and spillways and control structures, chevrons and wing dams and bendway weirs. The resulting edifice can barely be called a river at all, in any traditional sense. The Mississippi has been dredged, and walled in, and reshaped, and fixed; it has been turned into a gigantic navigation canal, or the world’s largest industrial sewer. It hasn’t run wild as a river does in nature for more than a hundred years. Its waters are notoriously foul. In the nineteenth century, the Mississippi was well known for its murkiness and filth, but today it swirls with all the effluvia of the modern age. There’s the storm runoff, thick with the glistening sheen of automotive waste. The drainage from the enormous mechanized farms of the heartland, and from millions of suburban lawns, is rich with pesticides and fertilizers like atrazine, alachlor, cyanazine, and metolachlor. A ceaseless drizzle comes from the chemical plants along the riverbanks that manufacture neoprene, polychloroprene, and an assortment of other refrigerants and performance elastomers. And then there are the waste products of steel mills, of sulfuric acid regeneration facilities, and of the refineries that produce gasoline, fuel oil, asphalt, propane, propylene, isobutane, kerosene, and coke. The Mississippi is one of the busiest industrial corridors in the world.