A few blogs back I spoke about the International Control Structure (ICS) located in the upper river above the falls. Associated with this structure are the two drive-in theatres like structures found along the shoreline above the ICS.
What you are looking at are the gates that open and close two tunnels 13.7 metres in diameter that carry water to the forebays of the Sir Adam Beck Generating Stations ten kilometres downstream at Queenston. The tunnels pass under the city of Niagara Falls, Ontario and they are about 101 metres below ground. They can transport water at 2850 cubic metres per second. Niagarans that have houses located above these tunnels say when it is really quiet outside they can hear the flow of water below their houses!
Two similar Hydro Gates are located in Niagara Falls, N.Y. These tunnels transport water to the reservoir above the Robert Moses Power Plant at Lewiston N.Y.