The Niagara Falls is a collection of three waterfalls at the south end of the Niagara Gorge, on the border between the Canadian province of Ontario and the US state of New York. Horseshoe Falls, the biggest of the three, which lies on the international border between the two countries, is also known as Canada Falls, while the smaller American Falls and Bridal Veil Falls are in the United States. Bridal Veil Falls is separated from Horseshoe Falls by Goat Island and from American Falls by Luna Island, both in New York. The falls, formed by the Niagara River flowing from Lake Erie into Lake Ontario, combined have the largest waterfall in North America, with a vertical drop of more than 50 meters. In addition to the beauty of Niagara Falls, it is also famous for its valuable source of hydroelectric power. Niagara Falls was formed when the glaciers retreated at the end of the Wisconsin glaciation and the newly formed Great Lakes water carved its way through the Niagara Escarpment on its way to the Atlantic Ocean. Starting at the base of Niagara Falls is Niagara Gorge, an 11 km long canyon carved out by the Niagara River on the border between Canada and the United States. Niagara Gorge ends at the edge of a geological formation called Niagara Escarpment. The river current in the gorge is one of the strongest in the world and kayaking in the gorge is generally prohibited because of the dangers involved.