One limestone ridge explains where the Great Lakes sit
The layout of the Great Lakes is no accident. A band of hard Niagara dolomite curves from New York through Ontario to Wisconsin, and the lakes fill the softer lowlands worn away on either side of it. The same ridge gives Niagara Falls its drop, and the region around it holds the world's largest freshwater system.
The Great Lakes region spans two countries: eight US states, from Minnesota and Wisconsin to New York and Pennsylvania, plus Ontario, with Quebec sometimes included because the St. Lawrence belongs to the same water system. It is a political grouping built on a narrow natural basin hemmed in by the Hudson Bay drainage to the north, the Mississippi to the west and the Ohio to the south. Its governors and premiers coordinate through a joint conference that also oversees agreements on sharing the basin's water.
The geology is layered like a tilted stack of books. Ancient Palaeozoic rock beds, hundreds of feet thick, dip gently south from the Laurentian Highlands of eastern Canada. Erosion carved low belts in the weak layers and left the tough ones standing as ridges. The chief ridge, the Niagara Escarpment, rarely rises more than 200 or 300 feet, but it runs unbroken from west-central New York, around Georgian Bay, between Lakes Superior and Michigan, and into Wisconsin before fading near the Mississippi. Lake Ontario, Georgian Bay and Green Bay lie in the lowland on its inner side; Erie, Huron and Michigan lie on the outer side. East of the escarpment the two lowlands merge into the Mohawk Valley, which became a vital trade route to the Atlantic in early US history.
Indigenous peoples have lived here since time immemorial. The Potawatomi organised political and cultural life around a seasonal round that adapted to changing conditions. European expansion pushed Native nations off their land and disrupted their ties to local ecosystems through industry and pollution, yet Anishinaabe and Potawatomi communities continue conservation work, including efforts to protect lake sturgeon.
Millions depend on the lakes, and they have paid for industrial growth. Farm runoff, sewage and factory waste have damaged water quality for decades, prompting large government responses. In 2014 both Toledo and Flint suffered drinking water crises, and those emergencies fell hardest on vulnerable minority communities.
Source: Great Lakes region
