Some people may not realize that between 9 pm and 8 am only 50% of the water that could go over Niagara Falls is diverted to produce electricity at hydro plants below the falls. The water is diverted by an open cut canal and tunnels located above the falls to these plants on both the U.S. and Canadian side of the border at Lewiston, New York and Queenston, Ontario. In the winter months another 25% is diverted allowing only one quarter of the water that could flow over Niagara Falls to do so.
To illustrate this fact I have taken a “before” and “after” photo of the water level at the Whirlpool a few kilometres below the falls.
The level of the shoreline after the water is diverted is about 6 metres (10 feet) lower. It takes about one hour to return to the “normal” daytime level.
The first photographs show the low level. The second set of photographs show the normal high level.