Overview of Transportation and the Lake

New Orleans is located where it is because of one and only one reason - the river. But the lake played a major role:

The French engineers, when examining the maps of Louisiana, emphatically wanted it located at what is pre- sent-day Baton Rouge. New Odeans, as far as they were concerned, was nothing more than a swamp located below sea level infested with alligators and mosquitos. John Law, on the other hand, was considering how the merchandise that would be shipped down the river would get into the Gulf of Mexico once it reached the port city.
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Another interesting fact about Lake Pontchartrain is that it is the nation's seventh largest lake.

John Law, the man who conceived of the City of New Orleans, knew that in order to control the economics of the Mississippi Valley, you had to control the traffic on the Mississippi and thus he convinced the Duke of Orleans to establish a city, naming it in his honor. He decided to locate it on the banks of the mighty Mississippi River as close to the Gulf of Mexico as possible which would allow freight to get into the Gulf even when the mouth of the river was closed.

Since the mouth of the Mississippi River was closed because of sand bars more than it was open until after the Civil War, John Law got his way, having the city located where it is, so that merchandise unloaded at the Port of New Orleans could be put on wagons and carried a very short distance to Lake Pontchartrain and from there ships could carry it through the Chef Pass into the Gulf of Mexico and onto the world's market.

http://gcrc.med.unc.edu:70/0/ftp/doc/neworl.txt