Lake Borgne  Lake Borgne () is a lagoon of the Gulf of Mexico in southeastern Louisiana. Although early maps show it as a lake surrounded by land, coastal erosion has made it an arm of the Gulf of Mexico. Its name comes from the French word "borgne", which means "one-eyed." In southern Louisiana, three large lakes—Maurepas, Pontchartrain, and Borgne—cover 55% of the Pontchartrain Basin. A brackish marsh land bridge and Lake St. Catherine separate Lake Pontchartrain from Lake Borgne. The Rigolets and Chef Menteur Pass are the two open water connections between Pontchartrain and Borgne. Due to coastal erosion, Borgne is now a lagoon connecting to the Gulf of Mexico. Early 18th-century maps show Borgne as a true lake, largely separated from the Gulf by a considerable extent of wetlands that have since disappeared. In a 1902 case before the United States Supreme Court over the oyster banks at the boundary between Louisiana and Mississippi, the State of Mississippi argued that at the time of Louisiana's admission into the Union, there probably was no such "Lake Borgne" or "Mississippi Sound". The basin contains 483,390 acres (1956 km²) of wetlands, consisting of nearly 38,500 acres (156 km²) of fresh marsh, 28,600 acres (116 km²) of intermediate marsh, 116,800 acres (473 km²) of brackish marsh, 83,900 acres (340 km²) of saline marsh, and 215,600 acres (873 km²) of cypress swamp. Since 1932, more than 66,000 acres (267 km²) of marsh have converted to water in the Pontchartrain Basin—over 22% of the marsh that existed in 1932. The primary causes of wetland loss in the basin are the interrelated effects of human activities and the estuarine processes that began to predominate many hundreds of years ago. The Mississippi River delta was abandoned by natural changes in the river. In response to the extensive damage from Hurricane Katrina in 2005, the Army Corps of Engineers constructed the 1.8-mile-long (2.9 km) IHNC Lake Borgne Surge Barrier, as part of the Hurricane and Storm Damage Risk Reduction System (HSDRRS) for southeast Louisiana. The project cost approximately $1.1 billion and was built at the confluence of the Gulf Intracoastal Waterway and the Mississippi River Gulf Outlet (MRGO).