During the past million years there were four glacial ages that covered the Rochester area with ice and impacted the geography of the area. The most recent glacier that left evidence here was about 100,000 years ago and it caused compression of the earth by as much as 2,500 feet (760 m). About 12,000 years ago, the area underwent massive changes, which included the rerouting of the Genesee River and other water bodies. Since the earth rebounded from the melting glaciers more rapidly in Canada than in New York, water from Lake Ontario was spilled over New York due to its lower elevation. During this time, the original outlet of the Genesee River was flooded out, creating Irondequoit Bay.
On a French map of the area from 1688 titled "Le Lac Ontario" Irondequoit Bay was referred to as the "swamp of the Senecas". Prior to the 1840s, the bay was known as "Teoronto Bay."