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Lake Pontchartrain is a large brackish body of water located in southern Louisiana, near the Gulf of Mexico. It is situated just north of the city of New Orleans. The lake has served as an important transit path for industrial and shipping companies for many years, and drivers heading into or out of New Orleans can now cross the lake using a pair of parallel bridges known as the Lake Pontchartrain Causeway. In 2005 Hurricane Katrina struck the area, causing the lake to overflow its bank and flood the city, resulting in substantial damage.
With a surface area of 640 square miles (1,658 square km), Lake Pontchartrain is one of the largest lakes in the United States (US). It has an average depth of just 9.8 feet (3 m). Together with numerous other lakes throughout the region, Lake Pontchartrain forms a massive estuary that covers large portions of Louisiana and Mississippi. Given the proximity to the Gulf of Mexico and the Mississippi River, as well as this estuary, the land in this area is virtually surrounded by bodies of water.
For centuries, the environmental conditions in and around Lake Pontchartrain have been deteriorating, resulting in a loss of biodiversity. According to the US Geological Survey, the lake is heavily polluted, and continues to increase in salinity each year. Stormwater runoff and industrial pollution pose a major threat to fish and wildlife, while erosion and wetland destruction around the lake have made these problems even worse.
Through the mid-20th century, visitors and locals were forced to drive around the lake, or take boats or ferry across. In 1956, a bridge spanning 23.8 miles (38.35 km) was constructed to allow drivers to cross the lake safely. The bridge connects the Louisiana towns of Metairie and Mandeville, and is recognized by many as the longest continuous bridge in the world. In 1969, a second span was added parallel to the first, forming the Lake Pontchartrain causeway as it is known today. Since its construction, drivers were required to pay a toll to cross the bridge, though this toll is only collected in one direction.
In 2005 the New Orleans area was struck by Hurricane Katrina, which caused devastation to the city and the surrounding region. Lake Pontchartrain surged over levees and walls designed to contain the lake water, and this water flooded into New Orleans. Inspectors later found that these levees were poorly constructed, and were not designed to contain the lake during a high-powered hurricane like Katrina.