Niagara Falls is not man-made, but it is man-managed to such a degree that it is often called the "world's most controlled waterfall." Geologically, the falls formed naturally 12,000 years ago via glacial melt. However, since the mid-20th century, humans have significantly altered the flow for hydroelectric power and erosion control. Under the 1950 Niagara Treaty, the U.S. and Canada agreed to "turn down" the falls at night and during the winter, diverting up to 75% of the water flow through massive underground tunnels to power turbines. During peak tourist hours, they "turn up" the flow to ensure the iconic aesthetic. Additionally, the American Falls were famously "shut off" in 1969 by the Army Corps of Engineers using a temporary dam to study the rock face and remove "talus" (fallen rocks) at the base. Furthermore, engineers have used underwater weirs and concrete reinforcements to slow the natural erosion rate from 3 feet per year to just a few inches, effectively "freezing" the falls in their current position for future generations.
The Niagara River is a river that flows north from Lake Erie to Lake Ontario. It forms part of the border between the province of Ontario in Canada and the state of New York in the United States. There are differing theories as to the origin of the river's name.