Niagara Falls spans the border between the United States and Canada and has one of the highest flow rates of any waterfall in North America. This natural wonder is a dramatic drop within a massive, interconnected hydrological system. The immense volume of water originates from the Great Lakes, a network of freshwater bodies that collectively represent the world’s largest surface freshwater system. The falls result from the difference in elevation between two specific lakes, channeling a constant supply of water toward the Atlantic Ocean.
The Immediate Conduit: Lake Erie and the Niagara River
The most direct source of the falls’ water is Lake Erie, the fourth largest of the Great Lakes, which drains into the Niagara River. This 58-kilometer (36-mile) river acts as the immediate channel, carrying the water north toward Lake Ontario. The river’s path includes a significant drop in elevation, which is the underlying source of the falls’ power.
The total difference in elevation between Lake Erie and Lake Ontario is approximately 99 meters (326 feet), with nearly half of that drop occurring at the falls themselves. As the river approaches, it splits around Goat Island, creating the three distinct cascades: Horseshoe Falls, American Falls, and Bridal Veil Falls. Horseshoe Falls, on the Canadian side, is the largest and accommodates the majority of the water flow. The enormous volume of water, rather than exceptional height, makes Niagara Falls impressive, with more than 168,000 cubic meters (5.9 million cubic feet) plunging over the crest line every minute during peak hours.
The Ultimate Source: The Great Lakes Watershed
The water flowing into the Niagara River represents the accumulated drainage of the vast Great Lakes watershed. This immense basin drains an area of approximately 684,000 square kilometers (264,000 square miles), encompassing much of the North American heartland. This entire system ensures the continuous supply that feeds the falls.
Lake Erie receives its water from the three upper Great Lakes: Superior, Michigan, and Huron, which are all connected by a series of rivers and channels. Lake Superior, the largest and deepest, feeds into Lake Huron, which flows toward Lake Erie. This cascade effect means the Niagara River carries the combined outflow of four of the five Great Lakes.
The Great Lakes system contains about 18 percent of the world’s surface freshwater supply, a volume largely composed of “fossil” water left over from the last Ice Age. Precipitation and groundwater continuously replenish the system. The sheer scale of the drainage basin sustains the massive average flow rate of the falls, providing a consistent water source year-round.
Regulating the Flow: Hydropower and Diversion
The energy generated by the water’s drop has been harnessed for hydroelectric power generation on both the Canadian and American sides of the border. Not all of the water from the Niagara River is allowed to flow over the falls; a significant portion is diverted upstream through canals and tunnels. This water feeds powerful generating stations, such as the Sir Adam Beck Station in Canada and the Robert Moses Niagara Power Project in the United States.
The management of this flow is governed by the 1950 Niagara Treaty between the two nations, which is overseen by the International Joint Commission (IJC). This treaty mandates specific minimum flow rates to preserve the falls’ scenic beauty, especially during tourist hours. During daylight hours in the tourist season (April 1 to October 31), the minimum flow over the falls must be at least 2,832 cubic meters per second (100,000 cubic feet per second).
At night and during the non-tourist season, the minimum required flow is reduced to 1,416 cubic meters per second (50,000 cubic feet per second), allowing for greater water diversion for power generation. Structures like the International Control Dam, located above the falls, regulate the amount of water dispatched between the power plants and the falls. This regulation balances the economic benefit of power generation with the preservation of the natural wonder.
The Water’s Final Destination
After plunging over the precipice, the water collects in the lower Niagara River Gorge, continuing its journey northward. The river flows rapidly through the 11-kilometer (7-mile) gorge, eventually emptying into Lake Ontario. Lake Ontario is the last and smallest of the Great Lakes.
The water’s path continues from Lake Ontario, which acts as a final reservoir for the Great Lakes system. The water exits the lake via the St. Lawrence River, its final major conduit. This river flows northeast, carrying the volume of Great Lakes water across the continent. Ultimately, the water reaches the Atlantic Ocean through the Gulf of Saint Lawrence, completing its cycle in approximately 15 hours.