On June 12th, 1969, the course of Niagara Falls history was changed forever as 27,000 tons of rock were dumped upstream to dam the portion of the Niagara River supplying water to the American Falls. The result was almost instantaneous - millions of gallons of water falling more than 175 feet each minute was suddenly nothing but a trickle.
Altogether, the American Falls was intentionally stopped between June 1969 and November 1969 by the U.S. Army Corp of Engineer to study boulders piling at the bottom of the falls and assess possible actions to remove them. Officials on both the U.S. and Canadian sides of the border thought the boulders piling at the base of the American Falls were unsightly.
The boulders at the base of the American Falls have accumulated over hundreds of years. However, there have been occasions where this occurred more rapidly: 76,000 tons falling to the base of the falls in 1931 and 185,000 tons in 1954.
After five months of studying the boulders, it was decided that none of them would be touched. In fact, a report five years later in 1974 would detail that the boulders below the falls were actually necessary to keep it in place.
The Army Corp of Engineers did, however, spend a significant amount of time working to strengthen the durability and lifespan of the American Falls through the implementation of bolts and anchors. These improvements were made near the brink of the falls and in the area of Luna Island.
Turning off the Niagara Falls was, and continues to be, looked at as a success by both the U.S. and Canadian governments to solidify the long-term future of the American Falls.