Pontchartrain, Lake, a shallow body of brackish water in southeastern Louisiana. New Orleans is on its southern shore. The lake, which is actually a bay of the Gulf of Mexico, is 41 miles (66 km) long and 25 miles (40 km) wide. It covers 635 square miles (1,645 km2).
Lake Pontchartrain is connected on the west to Lake Maurepas, and on the east to the Gulf of Mexico through Lakes Saint Catherine and Borgne. A canal joins the lake to the Mississippi River, five miles (8 km) to the south, and also to the Intracoastal Waterway. The 23.8-mile (38.3-km) Pontchartrain Causeway crosses the lake near its center. A bridge spans the narrow eastern part, joining New Orleans with Slidell.
