Which part of the Niagara Falls system straddles the international border between Canada and the U.S.?

Niagara Falls is located 27 kilometers (17 miles) north-northwest of Buffalo, New York, in the United States, and 69 kilometers (43 miles) south-southwest of Toronto, Ontario, in Canada. It is a waterfall system consisting of a group of three waterfalls at the southern end of the Niagara Gorge, spanning the border between the province of Ontario, Canada and the state of New York in the United States.

The largest of the three is Horseshoe Falls, also known as the Canadian Falls, which straddles the international border of the two countries. The smaller American Falls and third Bridal Veil Falls, lie within the United States. Bridal Falls is separated from Horseshoe Falls by Goat Island and from the American Falls by Luna Island, with both islands situated in the state of New York.

The entire waterway system is formed by the Niagara River, which drains Lake Erie into Lake Ontario.

Niagara Falls was formed when glaciers receded at the end of the Wisconsin glaciation (the last ice age), and water from the newly formed Great Lakes carved a path over and through the Niagara Escarpment en route to the Atlantic Ocean.

The enormous energy of Niagara Falls has long been recognized as a potential source of power. The first known effort to harness the waters was in 1750, when Daniel Joncaire (c. 1774-1771), a French army officer and interpreter in New France, built a small canal above the falls to power his sawmill.