Lake Pontchartrain
The broad brackish lake on the edge of New Orleans
Lake Pontchartrain spreads across about 630 square miles (1,630 km²) just north of New Orleans, a broad, shallow body of brackish water that is technically an estuary rather than a true lake, connected to the Gulf of Mexico through a chain of passes and the Mississippi Sound. Averaging only about 12 feet deep, it laps against the levees that protect the low, sinking city on its southern shore.
The lake is crossed by the Lake Pontchartrain Causeway, a pair of parallel bridges running nearly 24 miles from shore to shore — for decades recognized as the longest continuous bridge over water in the world. During Hurricane Katrina in 2005, storm surge driven across the lake overwhelmed the levees and canals along its edge, flooding much of New Orleans, a reminder of how tightly the city's fate is bound to the water at its back.