According to meteorologist Dave Baker, in his post How Much Water Fell From The Sky?, Lake Pontchartrain holds roughly 1.5 trillion gallons of water.
Lake Pontchartrain is a brackish water estuary located in southeastern Louisiana. It is the second largest saltwater lake in the United States covering approximately 630 square miles. The lake has an average depth of 12-14 feet with a maximum of 18 feet and is characterized with a gradual sloping bottom.
Lake Pontchartrain temperature ranges from 9°C in December to 34°C in June and August. Lake Pontchartrain is an oligohaline estuary meaning the salinity typically remains between 0-5 ppt although it can be higher during draughts or large influxes of water from the Gulf of Mexico.
Lake Pontchartrain lies in the heart of the Pontchartrain Basin and is a vast ecological system that is home to many different species of fish, birds, mammals, and plants. As well as being tremendously important habitat for local wildlife, it functions as the center of the region’s commercial and recreational fishing industries. See more at www.saveourlake.org.
Long before 'The New World' was 'discovered' Lake Pontchartrain's southern shoreline was a vibrant and vital area. Here's a brief summary of the history of the New Orleans lakeshore from Pontchartrain.net.