I worked on the Mississippi River 1979-1984. Though the level didn't get this low then, it has been before.
No one has ever really realizes the volume of commodities that travel the inland waterways. Each 200' x 35' grain barge holds as much grain as 13-15 covered hopper railroad cars. Each 20 barge southbound tow carrying grain carries 280 railroad cars of grain, each 25 barge tows carry 300 cars worth. The railroads are already carrying capacity. There are hundreds of towboats constantly making the approximately 10-day round trip from St. Louis to New Orleans. (most grain comes to St. Louis via the Upper Mississippi River and Missouri River pushed by smaller boats, then pushed by larger boats from St. Louis to NO, where the grain is loaded onto ships) Coal, ammonia, alcohol, molasses, human waste, various chemicals, and petroleum products also travel on the inland waterways.
A bright side is that due to the drought, there won't be as much grain to carry, so grain now stored in elevators that won't be shipped downriver will not affect storage of new grain as much. lol