Breakthrough of Mississippi River

Date: October 5, 1869 • Location: Minneapolis, United States

During construction of the Eastman tunnel in St. Anthony, Minnesota (now Minneapolis), the Mississippi River broke through the tunnel's limestone ceiling, nearly destroying Saint Anthony Falls.

The Eastman tunnel, also called the Hennepin Island tunnel, was a 2,000-foot-long (600 m) underground passage in Saint Anthony, Minnesota, dug beneath the Mississippi River riverbed between 1868 and 1869 to create a tailrace so water-powered business could be located upstream of Saint Anthony Falls on Nicollet Island. The tunnel ran downstream from Nicollet Island, beneath Hennepin Island, and exited below Saint Anthony Falls.