The Niagara River and the entire Great Lakes Basin of which it is a part, is a legacy of the last Ice Age. Close to 18,000 years ago, southern Ontario was covered by ice sheets 2-3 kilometers thick. As the ice sheets advanced southward they gouged out the basins of the Great Lakes.

The Niagara Falls we see today is a direct legacy of the Wisconsin Glaciation, the most recent period of the last Ice Age. Approximately 18,000 years ago, the entire region was buried under ice sheets nearly 3 kilometers thick. As the climate warmed and the glaciers began to recede northward around 12,500 years ago, the resulting meltwater filled the Great Lakes basins and sought an exit toward the Atlantic. This led to the birth of the Niagara River. The falls themselves first began to flow over the Niagara Escarpment (at present-day Queenston-Lewiston) about 10,000 to 11,000 years ago. Interestingly, the process was briefly stalled for 5,000 years when the meltwater was rerouted north, but full flow returned roughly 5,500 years ago. Since then, the falls have eroded over 11 kilometers southward from their original position to their current 2026 location, leaving behind the spectacular Niagara Gorge as a geological record of the ice's retreat.