The American Falls is one of three waterfalls that together are known as Niagara Falls on the Niagara River along the Canada-U.S. border. Unlike the much larger Horseshoe Falls, which lies almost completely in Canada, the American Falls is completely within the U.S. state of New York.
The height of the American Falls ranges between . This measurement is taken from the top of the Falls to top of the rock pile (talus). The height of the Falls from the top of the Falls to the river is .
The falls are viewable from a steep angle on the American side, where it is possible to approach to within several meters of the edge of the falls. One can view the falls from the bank of the river, as well as on Goat Island and Luna Island, which are accessible by a pedestrian bridge that crosses the rapids of the Niagara river upstream from the falls. The falls are viewable head-on from the Canadian side in Niagara Falls, Ontario.
The ledge of the American Falls is shaped in a modified "W" form, caused by numerous rockfalls over the past 150 years which have resulted in the huge mound of rock at its base. The most notable recent rockfall occurred in 1954 with the collapse of Prospect Point to the north.
To survey the rockfall and determine how to prevent the falls from becoming a series of rapids, the US Army Corps of Engineers completely blocked the flow of water over the American Falls fom June to November 1969. Results conflict as to whether tourist attendance that season was higher or lower than normal. Attendance increases were likely due to the news that the cataract was dried off; decreases in tourists could be attributed to the fact people thought both cataracts (the American and Horseshoe Falls) were dewatered that year. By December 1969, water was flowing over the American Falls again. In the mid-1970s, it was decided not to make alterations to the rock wall and remove the talus, citing the trend to allow nature to take its course.