In descending order of area, the lake is located in parts of six Louisiana parishes: St. Tammany, Orleans, Jefferson, St. John the Baptist, St. Charles, and Tangipahoa.

He was the French Minister of the Marine, Chancellor, and Controller-General of Finances during the reign of France's "Sun King", Louis XIV, for whom the colony of La Louisiane was named.

It is thought that this name originates from it being where a bridge (French: pont) crossed the river Mauldre on the ancient route from Lutèce to Chartres (chartrain).

[15] A team of experts assembled by The Nature Conservancy assessed the situation in 2004 and identified seven target habitat types in particular need of conservation management: bottomland hardwood forest, cypress swamp, relict ridge woodland, fresh/intermediate marsh, brackish/salt marsh, lake open water, and littoral submersed aquatic vegetation.

The bottomland hardwood forest and cypress swamp are suffering from a lack of freshwater input and sediment deposition owing to the levees upstream from the lake.

[17][18] As of 1995, the United States Geological Survey was monitoring the environmental effects of shoreline erosion, loss of wetlands, pollution from urban areas and agriculture, saltwater intrusion from artificial waterways, dredging, basin subsidence and faulting, storms and sea level rise, and freshwater diversion from the Mississippi and other rivers.

The lake provides numerous recreational activities for people in New Orleans and is also home to the Southern Yacht Club.

In the 1920s, the Industrial Canal in the eastern part of the city opened, providing a direct navigable water connection, with locks, between the Mississippi River and the lake.

In the same decade, a project dredging new land from the lake shore behind a new concrete floodwall began; this would result in an expansion of the city into the former swamp between Metairie/Gentilly Ridges and the lakefront.

After the storm, hurricane-protection levees were built along Lake Pontchartrain's south shore to protect New Orleans and nearby communities.

Experts using computer modeling at Louisiana State University after Hurricane Katrina have concluded that the levees were never topped but rather faulty design, inadequate construction, or some combination of the two were responsible for the flooding of most of New Orleans.

When Hurricane Katrina reached Category 5 in 2005, some experts predicted that the levee system might fail completely if the storm passed close to the city.

Although Katrina weakened to a Category 3 before making landfall on August 29 (with only Category 1-2 strength winds in New Orleans on the weaker side of the eye of the hurricane), the outlying New Orleans East area along south Lake Pontchartrain was in the eyewall with winds, preceding the eye, nearly as strong as those experienced in Bay St. Louis, Mississippi.

Canals near Chalmette began leaking at 8 am,[citation needed] and some levees/canals, designed to withstand Category 3 storms, suffered multiple breaks the following day (see Effects of Hurricane Katrina in New Orleans), flooding 80% of the city.

In this area, flooding was not the result of levee overtopping but was due to a decision by the governmental administration of Jefferson Parish to abandon the levee-aligned drainage pumping stations.

[24] This resulted in the reverse flow of lake water through the pumping stations into drainage canals which subsequently overflowed, causing extensive flooding of the area between I-10 and the lakefront.

[citation needed] On September 5, 2005, the Army Corps of Engineers started to fix levee breaches by dropping huge sandbags from Chinook helicopters.

[25] Aerial photography suggests that 25 billion US gallons (95,000,000 m3) of water covered New Orleans as of September 2, which equals about 2% of Lake Pontchartrain's volume.

[citation needed] Due to a lack of electric power, the city was unable to treat the water before pumping it into the lake.

It is unclear how long the pollution will persist and what its environmental damage to the lake will be, or what the long-term health effects will be in the city from mold and other contamination.