<P> Niagara Falls is famed both for its beauty and as a valuable source of hydroelectric power . Balancing recreational, commercial, and industrial uses has been a challenge for the stewards of the falls since the 19th century . </P> <P> The Horseshoe Falls drop about 188 feet (57 m), while the height of the American Falls varies between 70 and 100 feet (21 and 30 m) because of the presence of giant boulders at its base . The larger Horseshoe Falls are about 2,600 feet (790 m) wide, while the American Falls are 1,060 feet (320 m) wide . The distance between the American extremity of the Niagara Falls and the Canadian extremity is 3,409 feet (1,039 m). </P> <P> The peak flow over Horseshoe Falls was recorded at 225,000 cubic feet (6,400 m) per second . The average annual flow rate is 85,000 cubic feet (2,400 m) per second . Since the flow is a direct function of the Lake Erie water elevation, it typically peaks in late spring or early summer . During the summer months, at least 100,000 cubic feet (2,800 m) per second of water traverses the falls, some 90% of which goes over the Horseshoe Falls, while the balance is diverted to hydroelectric facilities . This is accomplished by employing a weir--the International Control Dam--with movable gates upstream from the Horseshoe Falls . The falls' flow is further halved at night, and, during the low tourist season in the winter, remains a minimum of 50,000 cubic feet (1,400 m) per second . Water diversion is regulated by the 1950 Niagara Treaty and is administered by the International Niagara Board of Control (IJC). </P> <P> The verdant green colour of the water flowing over the Niagara Falls is a byproduct of the estimated 60 tonnes / minute of dissolved salts and "rock flour" (very finely ground rock) generated by the erosive force of the Niagara River itself . The current rate of erosion is approximately 1 foot (0.30 m) per year, down from a historical average of 3 feet (0.91 m) per year . It is estimated that 50,000 years from now, even at this reduced rate of erosion, the remaining 20 miles (32 km) to Lake Erie will have been undermined and the falls will cease to exist . </P>

Which of the great lakes flows into niagara falls