Motor Vessel MISSISSIPPI emerges from the early morning fog as she approaches Lock and Dam 6 in Trempeleau, Wis. Motor Vessel MISSISSIPPI emerges from the early morning fog as she approachs Lock and Dam 6 in Trempeleau, Wis. The largest diesel towboat on the Mississippi River was on the Upper Mississippi River as part of the Mississippi River Commission's Low Water Inspection trip. A public hearing was hosted by the Mississippi River Commission and Corps of Engineers onboard the Motor Vessel MISSISSIPPI at Riverside Park Landing in La Crosse, Wis., August 12, 2013.