Glacial Lake Algonquin

Lake Algonquin was a proglacial lake that existed in east-central North America at the time of the last ice age. Parts of the former lake are now Lake Huron, Georgian Bay, Lake Superior, Lake Michigan and inland portions of northern Michigan.

The lake varied in size, but it was at its biggest during the post-glacial period and gradually shrunk to the current Lake Huron and Georgian Bay. About 7,000 years ago, the lake was replaced by Lake Chippewa as the glaciers retreated and 3,000 years later by the current Lake Michigan.

About 11,000 years before present, the Laurentian Glacier has retreated northward, forming a boundary across the northern edges of Lake Superior and Lake Huron. The water level was at 605 feet (184 m) above sea level, creating a single body of water in the three basins of Lake Michigan, Lake Huron and Lake Superior. The lake drained through three outlets, the Chicago Outlet River, the St. Clair-Detroit River, and through the Trent Valley.

The first stage occupied only the south part of the basin of Lake Huron, including Saginaw Bay. It received tributary drainage from smaller lakes in the south part of the Georgian Bay and Lake Simcoe basins. Its existence is based on evidence of the establishment and erosion of its outlet through the distributaries of the St. Clair River at St. Clair, and on characters of the Niagara River and gorge. The steps of transition following this are simply physical and logical necessities, made so by the conditions of development from the first stage to the later fully developed Lake Algonquin, which included all three of the upper Great Lake basins.

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