In the summer of 1969, people started to notice that something was off with the Niagara Falls. The rocks at the top began to erode, and a large number of stones had accumulated at the bottom of the falls. Scientists realized that if nothing was done soon, the Niagara Falls was going to be in serious trouble.
Until engineers constructed the temporary dam in 1969, no one had seen the bare rock face of American Falls since March 30, 1848, when an ice jam from Lake Erie stopped the Niagara River. Source: smithsonianmag.com
Soon it was announced that engineers were going to drain the American side of the falls for six months. While townspeople wondered how they were going to get through a tourist season with no tourists, people from all around the world began wondering what lay hidden beneath the roaring waters. But nobody was prepared for what was actually found at the bottom.