Irondequoit Bay

Irondequoit Bay O-nyiu-da-on-da-gwat
View from Lucien Morin Park in Penfield, New York
Coordinates	43°12′18″N 77°31′52″W / 43.205°N 77.531°W / 43.205; -77.531Coordinates: 43°12′18″N 77°31′52″W / 43.205°N 77.531°W / 43.205; -77.531
Type	Bay
Etymology	"It turns out"/"It goes aside"
Primary inflows	Densmore Creek, Irondequoit Creek
Primary outflows	Lake Ontario
Managing agency	New York State Department of Environmental Conservation
Max. length	4 miles (6.4 km)
Max. width	0.5 miles (0.80 km)
Surface area	1,660 acres (670 ha)
Max. depth	73 feet (22 m)
Shore length1	17.7 miles (28.5 km)
Surface elevation	250 feet (76 m)
Islands	Fish Island, Held Island, Snider Island
Settlements	Irondequoit, Penfield, Webster
1 Shore length is not a well-defined measure.

Irondequoit Bay is a large body of water located in northeastern Monroe County, New York. The bay, roughly 0.5 miles (0.80 km) wide and 4 miles (6.4 km) in length, is fed by Irondequoit Creek to the south and flows into Lake Ontario at its northern end. On average, the surface of Irondequoit Bay rests at 245 feet (75 m) above sea level and is 80 feet (24 m) deep at its deepest point a short distance north of the Irondequoit Bay Bridge carrying the six-lane New York State Route 104 over the bay.

The center of the bay acts as the eastern border for the town of Irondequoit and the western border of the towns of Penfield and Webster. The Irondequoit–Penfield boundary continues along the center of Irondequoit Creek south of the New York State Route 404 float bridge.

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."