Engineers shut off the American side of Niagara Falls for five months in 1969 to inspect the rock underneath
The U.S. Army Corps of Engineers built a temporary rock-and-earth cofferdam above the American Falls, diverting the water toward Horseshoe Falls. The American Falls remained dewatered from June 12 until November 25 while engineers mapped the riverbed, drilled test cores and studied erosion and rockfall. Nearly 28,000 tons of fill went into the temporary dam.
u/hamzapsy13 — 2 days ago