| Lock and Dam No. 9 | |
| Location Map: | Wisconsin |
| Dam Crosses: | Upper Mississippi River |
| Res Name: | Pool 9 / Lake Winneshiek |
| Location: | Taylor Township, Allamakee County, Iowa / Seneca, Crawford County, Wisconsin, near Lynxville, Wisconsin, USA |
| Operator: | U.S. Army Corps of Engineers, St. Paul District |
| Opening: | July |
| Res Capacity Total: | 470000acre feet |
| Res Catchment: | 66610mi2 |
| Coordinates: | 43.2128°N -91.1042°W |
Lock and Dam No. 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 620feet. It was constructed and placed in operation in July 1937. The site underwent a major rehabilitation from 1989 and 2006. The dam consists of concrete structure 811feet long with five roller gates and eight tainter gates. Earth embankment 9800feet long with a grouted overflow spillway 1350feet long. The lock is 110feet wide by 600feet long. Lock and Dam No. 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.