The fresh water that plunges over Niagara takes around 685,000 gallons (2.6 million litres) of water from four great lakes: Lake Superior, Lake Michigan Lake Huron and Lake Erie - in fact, ? of the world's fresh water is found in these four great lakes.

The water that powers Niagara Falls originates from the upper Great Lakes basin, specifically draining from Lake Superior, Lake Michigan, Lake Huron, and Lake Erie. This vast system represents approximately 20% of the world's total freshwater supply. The water flows from Lake Erie through the 35-mile-long Niagara River, which acts as a natural connecting channel to Lake Ontario. Before reaching the precipice, the water is split by Goat Island into the American Falls and the Horseshoe Falls. Interestingly, the flow is highly regulated by the 1950 Niagara Treaty between the United States and Canada; during the peak tourist season in 2026, roughly 100,000 cubic feet per second are allowed over the falls, while the rest is diverted through massive tunnels to hydroelectric power plants like the Sir Adam Beck Station. This diversion generates enough electricity to power millions of homes. Once the water plunges over the falls, it continues through the Niagara Gorge into Lake Ontario and eventually flows out through the St. Lawrence River into the Atlantic Ocean, completing a journey that began deep in the North American interior.