Lake Pontchartrain (local English pronunciation leɪk ˈpʰɑntʃətʰɹeɪn) French: Lac Pontchartrain, pronounced lak pɔ̃ʃaʀtʀɛ̃) is a brackish lake located in southeastern Louisiana. It is the second largest salt-water lake in the United States, after the Great Salt Lake in Utah, and the largest lake in Louisiana. It covers an area of 630 square miles (1630 square km) with an average depth of 12 to 14 feet (about 4 meters). Some shipping channels are kept deeper through dredging. It is roughly oval in shape, about 40 miles (64 km) wide and 24 miles (39 km) from south to north. The south shore forms the northern boundary of the cities of New Orleans, Louisiana, and its two largest suburbs Metairie, Louisiana and Kenner, Louisiana. On the north shore are the cities of Mandeville, Louisiana, Covington, Louisiana, and Madisonville, Louisiana. To the northeast is the city of Slidell, Louisiana.

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