Louisiana Files #002 Many people call every body of water in Louisiana a "bayou." But bayous, swamps, and marshes aren't the same thing. A bayou is a slow-moving waterway, often winding through forests and wetlands. A swamp is a forest that stays flooded for much of the year, filled with towering cypress trees and hanging Spanish moss. A marsh is open wetland dominated by grasses instead of trees. The Atchafalaya Basin, stretching across south-central Louisiana, is the larges