During the early 20th century, the Atchafalaya River Basin was designated as a spillway for floods of the Mississippi River. In order to facilitate this emergency plan without flooding adjacent agriculture and towns, protective levees were built dividing the Atchafalaya Basin Floodway from large portions of the historic swamp boundaries. A central channel was dredged through some existing channels and in some places through swamp forest. At that point the isolated Atchafalaya River Basin was permanently connected to a very large, sediment-rich river.