In the upper river, within view of Niagara Falls, is a large structure that looks like half a bridge. This is the international control dam. Since 1954, it regulates how much water goes over Niagara Falls and how much is diverted beforehand for hydro-electric power.This control dam allows water from the upper river to be diverted into the intakes for the American and Canadian power stations. Two tunnels on the American side take water under the town of Niagara Falls, New York and three tunnels on the Canadian side divert water under the town of Niagara Falls, Ontario. Once passed these cities, the water flows into two canals and then into two large reservoirs. Behind the Canadian Sir Adam Beck powerplant is a reservoir covering 300 hectares (750 acres) and a similar reservoir on the US side behind the Robert Moses Station.A trade off exists between the two main industries of Tourism and Hydroelectric Power. More water is diverted by the International Control Dam at night, between 10 pm and 7:00 am, filling the reservoirs over night, and allowing more water over Niagara Falls in the day-time hours for the tourists. As well, during the winter, from Nov. 1 to March 31, when it is not the tourism season, more water is diverted for electrical power during the whole 24 hour period.