Water surrounding greater metropolitan New Orleans is featured in this north-looking photograph. Apparent are Lake Maurepas, the small body of water to the west that flows into Lake Pontchartrain, and Lake Salvador, the large lake south of New Orleans. The 24-mile (39-kilometer) causeway that connects New Orleans with communities on the north shore of Lake Pontchartrain bisects this large, relatively shallow lake whose average depth is 12 feet (3.6 meters). Most of the darker areas are standing water, swamps, and marshlands; the dark, linear features are canals. The meandering Mississippi River is easily discernible as it flows south to the Gulf of Mexico.