The Eastman tunnel, also called the Hennepin Island tunnel, was a 2,000-foot-long (600 m) underground passage in Saint Anthony, Minnesota (now Minneapolis), 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 rushing river scoured the tunnel, caving in parts of Hennepin Island and causing the earth supporting Saint Anthony Falls to collapse upstream.

The final fix for the tunnel disaster was a concrete dike constructed by the United States Army Corps of Engineers.

[4][5] [6] [7] For the next year, workers dug in the soft sandstone beneath the thin layer of limestone that forms the river's bed.

[4] The rushing river scoured the tunnel, caving in parts of Hennepin Island and causing the earth supporting Saint Anthony Falls to collapse upstream.

[2][4] There was immediate, serious concern that the riverbed would crumble and reduce Saint Anthony Falls to a long set of rapids.

[4] One witness remembered, "Proprietors of stores hastened to the falls, taking their clerks with them; bakers deserted their ovens, lumbermen were ordered from the mills, barbers left their customers unshorn; mechanics dropped their tools; lawyers shut up their books or stopped pleading in the courts; physicians abandoned their offices.

[4] Within a few weeks, the plug held and dams were built to divert the river and stop Saint Anthony Falls from being washed away.

[5][3] The apron stopped the upstream progression of the falls (which was a separate problem from the tunnel) and prevented damage from logs that escaped from the then prevalent sawmills.

"[15] The tremendous damage caused by the Hennepin Island tunnel brought lawsuits and demands for political change.

[2] To the relief of the local population, the United States Army Corps of Engineers made the repairs using federal money on the pretext that it was protecting navigation.