Great Lakes

The basic structure of the Great Lakes was formed by glacial action during the Pleistocene epoch (see also Ice Ages). Before then, the area now occupied by Lake Superior was made up of broad valleys and river systems, and the present region of the other lakes was probably a plain. During the Ice Age, glaciers moved southwards, deepening the valleys of the Lake Superior region and gouging depressions in the low plains to form the beds of the other lakes. When the glaciers retreated, fingers of ice were left in these depressions, and as the ice melted further, lakes were formed. The drainage patterns of the lakes region were altered later by successive advances and retreats of ice caps, until the most recent retreat and subsequent uplifting of the northern part of the area caused the lakes to empty into the St Lawrence River.

The Great Lakes region was home to numerous Native American groups, such as the Algonquin, Iroquois, Ojibwa, and Huron, who fished its waters and operated trade networks extending from present-day Minnesota to New York. The first Europeans to travel on the lakes were French missionaries and explorers between the mid-1500s and mid-1600s, such as Jacques Cartier, Étienne Brûlé, Samuel de Champlain, and Jean Nicolet. Their travels opened up the fur trade, which exploited the lakes as a transport route to carry pelts by canoe from the interior to Atlantic ports. As early as the 1620s the French exerted control of the western margins of Lake Superior, establishing a fort at Detroit and tapping fur resources from Québec, in the east, to western Ontario and Minnesota, in the west.

During the War of 1812, naval battles between the United States and Britain took place on Lakes Ontario and Erie. Since then, lake-based commerce has developed peacefully. The lakes were an important route for westward expansion of European settlement during the early 1800s. The Welland Ship Canal was opened in 1829, and the first significant canals at Sault Sainte Marie were built in the 1850s. By the late 1800s lake ports such as Chicago, Milwaukee, Detroit, Cleveland, Buffalo, Toronto, and Hamilton were thriving industrial cities linking the interior of the continent with the Atlantic seaboard. The St Lawrence Seaway strengthened this link by permitting ocean-going vessels to travel between the lakes and the Atlantic.