SIX GIANT BENDS IN THE MISSISSIPPI from Baton Rouge, in the town of Geismar, I zip past the abandoned hulk of the Workshop Lounge, a strip joint destroyed not by foul weather, I'm guessing, so much as lack of big spenders in this part of the state. It seems naked ladies are in less demand these days than "specialty chemicals." That's what they're busily manufacturing, amid spewings of dense white smog, at the mammoth Hexion plant across the river road, which is obscured by a column of stalled traffic.

Stuck in their sluggardly vehicles, those folks don't even see me flying along up here. I'm all alone: no cyclists, joggers, or strollers. Not even a disaster gawker, the newest species of tourist to swarm the Gulf Coast. But there's not that much to gawk at around here: Though this neck of the river swelled at least 12 feet in the three hours after Katrina first ran into the Mississippi 130 miles or so south of here—the water rose about 20 feet at that spot—the storm didn't make it here, sparing southern Louisiana a toxic-chemical bath of apocalyptic proportions. The sense of relief was apparently so overwhelming that nobody's much mentioned that the hurricane successfully swamped a few refineries to the east of New Orleans, dumping 170,000 barrels of oil—much of it into Louisiana's ailing wetlands. (This volume, though not to be sniffed at, pales in comparison to one of history's worst oil spills, the Ixtoc I exploratory well's hemorrhaging of an estimated 3,333,333 barrels into the Gulf of Mexico from June 1979 to March 1980).

Having chased the river for going on 40 miles now, I have yet to share any of T.S. Eliot's sense of fearful wonder when he described it as "a strong brown god," in his poem "The Dry Salvages." Lying flat on its back beneath a groaning oaf of a barge grinding through the channel, the river strikes me as more of a rough old whore—a one-eyed, gap-toothed, 400-pound truck-stop hooker with a mustache who, if she could just get free of her pimp, would stomp every ass in the land. The weary receptacle of countless kiloliters of ignoble fluids pouring from every urban gutter, cornfield, and industrial sump from here to Minnesota, the Mississippi inspires considerably less divine awe than the federal levee system itself, a 1,607-mile network that's arguably the most astounding feat of human brilliance and insanity this side of the Bomb. The Great Wall of China—what, repelled a few thousand Huns? This monster has survived a three-century assault by the third-largest river system in the world with only a few famous ruptures. Millions of people live under its protection. The Great Pyramid couldn't even protect its solitary ward from the sanctioned thievery of prying archaeologists.

Over countless millennia, the Mississippi River made Louisiana out of eroded fragments of no less than 30 other states, whose soils once tumbled south to spill across bayou country when the river jumped its banks. But with its flooding rights revoked by levees—from 1718 to 1803, the French used increasing amounts of slave and immigrant labor to shackle the river from Baton Rouge on down—the Mississippi vomits earth that might otherwise become Louisiana wetlands into the Gulf of Mexico at a ridiculous rate. (On average, 40 acre-feet get dumped before you've had your coffee.) Since 1932 alone, 2,117 miles of Louisiana coastline has vanished, with 34 additional miles sloughing off each year. And everybody knows the best flood-protection system at Louisiana's disposal is not the levee system but the wetlands, which shrink storm surges by a foot for every 2.7 miles traversed.

Before the levees were in place, hundreds of square miles of wetland stood between Lake Borgne, on New Orleans's eastern flank, and the Gulf of Mexico. Think about it. Its enclosing wetlands deprived of sediment for over two centuries, the lake is now little more than a scalloped embayment on the Gulf's shore. When Katrina hit, a 15-foot wall of water surged through Lake Borgne, toppling floodwalls and pretty much annihilating the Lower Ninth Ward and New Orleans East. Had the Mississippi never been leveed, the storm surge wouldn't have hit the city at such lethal heights, but, of course, without the levee there would have been no city for the surge to spare.