Corps levees look like ordinary hills along the riverbank, but they have severed the Mississippi from more than 90 percent of its floodplain, eliminating millions of acres of wetlands that had attracted fish, shorebirds and other wildlife. Dams and dikes that stabilized the main barge channel have degraded biologically diverse back channels. The river's water quality has deteriorated steadily, pouring pesticides into the Gulf of Mexico's oxygen-deprived "dead zone." And changes in sediment flows have depleted Louisiana's coastal marshes, which are vanishing so fast that some experts are calling for a restoration project twice the size of the Everglades mission.

Overall, the Corps predicted the project will only eliminate 167 acres of wetlands overall, an estimate [Tim Searchinger] said was "directly contradicted" by the agency's own data. The Corps acknowledged that it would reduce flooding on 8,000 acres of forested wetlands and 28,000 acres of agricultural wetlands. By contrast, in its regulatory role under the Clean Water Act, the Corps permitted more than 4,000 development projects last year, affecting less than 22,000 acres of wetlands.

Environmentalists point out that the floodway was never supposed to attract a revival; it was supposed to remain undeveloped. That's the flip side of Corps flood control projects: They can instill a false sense of security, luring pioneers into floodplains, accelerating demands for even more protection. Despite $100 billion worth of Corps projects, flood emergencies, damages and deaths are on the rise, and the federal government is spending more money than ever to move Americans out of harm's way. Meanwhile, most of the wetlands of the Mississippi basin have been drained by farmers or paved by developers, often with Corps permits. That means that most of the runoff from 31 states and two Canadian provinces now flows straight to the river, which means that it takes less water to create a horrific flood.