There are actually three falls; the American and Bridal Veil Falls and the Canadian Horseshoe Falls. The U.S. owns the first two and the Canadian Horseshoe Falls is owned by Canada.
Ten percent of the Niagara River flows over the American and Bridal Veil Falls and the remaining 90% over the Canadian Horseshoe Falls. During the winter months, from midnight to 7 a.m. 75% of the water is diverted from going over the falls to create hydro electricity. During the summer months the flow of water going over the falls is increased to 50%.