Lower Mississippi River
When talking about the Lower Mississippi River, it's the section downriver from the confluence of the Ohio River and Mississippi River at Cairo, IL, all the way to the delta, about 1,000 miles.
There are no locks and dams like on the Upper Mississippi River, however the river is constrainedby levees and dikes for flood control and to maintain a safe navigation channel for the towing industry.
The first steamboat on the Lower Mississippi River was Fulton's NEW ORLEANS in 1811, coming from Pittsburgh, PA, down the Ohio River all the way to New Orleans. From 1812 to 1814 the NEW ORLEANS ran in the New Orleans - Natchez trade successfully. The Vesuvius (1814), Aetna (1815) and the second New Orleans (1815) were built and placed in operation very soon. The Aetna and later the Vesuvius ran not only to Natchez but successflly in the New Orleans - Louisville trade, where Fulton had a monopoly for quite a while.
Steamboats on the Western Rivers, Louis C. Hunter
The Mississippi Steamboat Era in Historic Photographs, Joan W. and Thomas H. Gandy