To preserve Niagara Falls' natural beauty and to ensure an "unbroken curtain of water" is flowing over the falls, the 1950 treaty was signed by the U.S. and Canada to limit water usage by power plants.

[1] The treaty states that during daylight time during the tourist season (April 1 to October 31), there must be 2,800 cubic metres per second (99,000 cu ft/s) of water flowing over the falls, and during the night and off-tourist season there must be 1,400 cubic metres per second (49,000 cu ft/s) of water flowing over the falls.

This weir 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 city of Niagara Falls, New York, and three tunnels on the Canadian side divert water under the city of Niagara Falls, Ontario.

As well, during the winter, from November 1 to March 31, when it is not the tourism season, more water is diverted for electrical power during the whole 24 hour period.