The Niagara River flows from Lake Erie to Lake Ontario forming a natural boundary between Canada and the United States. The river's most prominent feature is Niagara Falls; 90 percent of the river's volume flows over the Canadian Horseshoe Falls. Boats ply the river below it daily from April to October. Grand Island, the island largest in the river, is in US waters. Thirty local and state park areas front the river on both sides of the border.