Every second, around 28 million litres (700,000 gallons) of water flow down Niagara Falls. It is believed to be the fastest-moving waterfall in the world. With a height of 188 feet (57 meters) and a depth of 170 feet (52 meters), Horseshoe Falls is the tallest waterfall. Glacier action caused Niagara Falls to develop some 12,000 years ago.