The Niagara Falls are produced because the Niagara River is prevented from eroding its bed by a band of hard limestone rock.

The Horseshoe Falls 188ft (57m) high and 2,600ft (790m) wide. The falls are part of the Niagara River, which is the outlet from Lake Erie. The green water is produced by dissolved salts. The falls retreat by 3ft (1m) per year. In 50,000 years the falls will have retreated all the way to Lake Erie.

The American Falls at Niagara are 830ft (250m) wide and fall about 100ft (30m) to the rocks below. The depth of water over the falls is 2ft( 60cm) deep. The rocks are the remains of the lip of the waterfall, whose rocks frequently break away.

THE NIAGARA FALLS - BY BOAT!
One of the most dramatic ways of seeing Niagara is by the Maid of the Mist boat.

The boat travels up the gorge to the plunge pool (which some call a whirlpool) below the Horseshoe Falls (Canadian Falls), passing the American Falls on the way.

The mist is created by the water falling vertically from the waterfall lip. The plunge pool is made by rocks carried in the water, falling (plunging) down from the waterfall lip, and then hitting the gorge floor, so wearing it into a deep pool.