Mississippi River Lock and Dam 9, also known as Lock & Dam 9 (Winthrop Rockfeller), is a concrete run-of-river dam located in Prairie du Chien, Wisconsin. Completed in 1937, this federal-owned structure primarily serves for navigation purposes along the Mississippi River. With a dam height of 18 feet and a hydraulic height of 32 feet, it maintains a constant pool level for river traffic at elevation 619.3, with a maximum discharge capacity of 278,000 cubic feet per second.

Despite being classified as a low-risk dam by the US Army Corps of Engineers (USACE), Lock & Dam 9 faces potential hazards related to the aging miter gates in the locks and the risk of navigation accidents. USACE actively manages these risks through continuous monitoring, prioritizing maintenance activities, and engaging with the public to raise awareness of the dam's presence and potential dangers. The dam's spillway is regulated to control pool levels and can handle flows up to 63,000 cfs, with a maximum water level differential of 9 feet at low river flows. With a risk assessment rating of Very High (1), USACE remains vigilant in ensuring the safety and functionality of Lock & Dam 9 for both navigation and public safety.