The water that goes over the falls drains an area of 6.837 square metres (264,000 square miles) including Lakes Erie, Michigan, Huron and Superior.
After flowing down, the Niagara River (which runs between Lakes Erie and Ontario) it empties into Lake Ontario and eventually into the St. Lawrence River and out into the Atlantic Ocean.
The drop-in elevation between Lakes Erie and Ontario is 99 metres (325 feet). That’s the reason why you find the Welland Canal here. The canal includes 8 locks that gradually takes the ships up or down from one lake to the other. If this canal didn’t exist the ships could not by-pass the falls of Niagara.