According to the Corps’ assessment, reimposing “hydrologic separation” would, indeed, be the most effective way to keep carp out of the Great Lakes. It would also, in the Corps’ estimate, take twenty-five years—three times as long as the original digging of the canal had—and cost up to $18 billion. Many experts I spoke to said the billions would be money well spent. They pointed out that each of the two drainage basins has its own roster of invasives, some, like the carp, brought over intentionally, but most introduced accidentally, in ballast water.
