Hennepin Island tunnel was a 2,500-foot (760 m)-long underground passage in Saint Anthony, Minnesota (now Minneapolis) dug beneath the Mississippi River riverbed between 1868 and 1869 to create a downstream spillway for hydro plants, milling and lumber business located upstream of St. Anthony Falls. The tunnel ran downstream from Nicollet Island, beneath Hennepin Island, and exited below St. Anthony Falls. The site of the tunnel is about a mile upstream from the 2007 collapse of the I-35W Mississippi River bridge.