Niagara Falls. Aerial view of a rainbow rising out of the mist formed by the Niagara Falls, seen from the Canadian side of the American-Canadian border. Seen here is the Canadian Horseshoe Falls, the larger of the two main falls. The Horseshoe Falls, in Ontario province, is 49 metres (m) high and 790 m long along the crest. About 5.5 million litres of water are carried over the Niagara Falls each second, of which about 90% flows over the Horse- shoe Falls. This water is eroding the Horseshoe Falls at about 1.5 m every year. The falls occur where the Niagara River passes over erosion- resistant rock underlain with softer material. The Falls are a major tourist attraction.