American Falls is one of the three waterfalls of Niagara Falls on the Niagara River at the Canada–United States border, and the only one lying entirely within the United States at Niagara Falls, New York. Separated from Horseshoe Falls by Goat Island, it is the second largest of the three and carries about 11 percent of the river’s flow. Repeated rockfalls over the past 150 years reshaped its brink into a modified W and created the large talus at its base. After a notable collapse at Prospect Point in 1954, the U.S. Army Corps of Engineers shut off the water in 1969 to study erosion, then later chose to let natural processes continue.