Nipissing Great Lakes

Nipissing Great Lakes was a prehistoric proglacial lake. Parts of the former lake are now Lake Superior, Lake Huron, Georgian Bay and Lake Michigan. It formed about 7,500 years before present (YBP). The lake occupied the depression left by the Labradorian Glacier. This body of water drained eastward from Georgian Bay to the Ottawa valley. This was a period of isostatic rebound raising the outlet over time, until it opened the outlet through the St. Clair valley.

The Lake formed from the aggregation of Glacial Lakes Houghton, Chippewa and Hough, and Stanley as water levels increased. Levels returned and Lake Chippewa again flowed through the canyon at Mackinac until around 7,500 YBP. At that time, the waters in the Michigan basin, Huron basin, and the Superior basin created a single lake encompassing all three of the upper Great Lakes. The lowlands through the rapids of Sault Ste. Marie and across the Upper Peninsula of Michigan were open bodies of water.

The term "Nipissing Great Lakes" is applied to the waters of the upper three Great Lakes during the stage. The glacier had receded completely from the Great Lakes Basin. The plural form is used to denote that each basin was a separate unit, with a narrow strait connecting each. Each basin stood at the same elevation and thus appear as a single body of water. Lake Michigan connected to Lake Huron by the Mackinac strait, except the water was 50 feet (15 m) higher. There was also a narrower, shallower channel Little Traverse Bay to Huron basin. The outlet of the lakes, however, was eastward from the northeast angle of Georgian Bay.

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