9 is an American lock and dam located near Lynxville, Wisconsin and Harpers Ferry, Iowa on the Upper Mississippi River around river mile 647.9.

The lower portion of Pool 9 was formally named Lake Winneshiek.

The normal pool elevation behind the dam is 620 feet (189.0 m).

9 is located 12 miles upstream from Prairie du Chien, Wisconsin.

[1] The lock and dam are owned and operated by the St. Paul District of the United States Army Corps of Engineers-Mississippi Valley Division.