III. Geography

The Great Lakes

 Lake Michigan pier, St. Joseph, Michigan.   
Photo by Sathyan Sundram.

 

      The largest supply of inland fresh water in North America is made up of five major lakes (Erie, Huron, Michigan, Ontario and Superior) and one minor lake (St. Clair). The Great Lakes were formed 12,000 years ago during the last period of glaciation (Ice Age) when massive glaciers extended across the region and gouged troughs into the landscape. As the glaciers receded, these depressions filled with melt water. Today the Great Lakes cover 94,250 square miles and contain 18% of the world’s fresh water. 

     The lakes and the St. Lawrence River form an inland waterway connecting the Atlantic Ocean with the interior of North America. Stretching from Duluth, Minnesota on Lake Superior (average lake surface elevation of 600 feet above sea level) to the Atlantic, the Great Lakes-St. Lawrence seaway extends 2342 statute miles through four connecting river systems and nineteen lift locks. As a vital transportation linkage, the Great Lakes facilitate global trade in grain commodities, iron and coal products. The waterway connects the natural resources and manufacturing cities of Minnesota, Wisconsin, Michigan, Indiana, Illinois, Ohio, Pennsylvania, and New York. Canals have extended this network to connect the Hudson River and Mississippi River inland waterways.
 
     The Great Lakes provide important water resources for cities and offer recreation space for their inhabitants. Three of the United States major industrial centers and most populous metropolitan areas are located in the region: Chicago on Lake Michigan, Detroit between Lakes Erie and St. Clair, and Cleveland on Lake Erie. Though no major commercial fisheries exist currently, the lakes were a significant supplier of fish for Native Americans and early European settlers. Past industrial and agricultural water pollution and exogenous species such as lampreys and zebra mussels have severely damaged native fish populations and, subsequently, their predators. Since the mid-twentieth century, the Great Lakes have been stocked with a number of oceanic fish species, such as Steelhead and Coho salmon, which flourish and spawn in tributary rivers. Today, recreational fishing and boating draw millions of tourists to the region annually, although some fish species such as Walleye are still considered unsafe to eat due to chemical contamination.
 
     The Great Lakes area is an important agricultural region. Sandy soils rich in glacial till, the sedimentary remnants of receding glaciers, that line the coastal plains along the southern and eastern lakeshores are well suited for staple crops, mainly corn and soybeans. A variety of specialty crops such as cherries, asparagus, apples and grapes benefit from the more temperate climate along the lakeshores, where changes in air temperature are less extreme due to the thermal mediation of the large water bodies. Thus, the lakes provide an extended frost-free growing season and the rootstock of perennial plants is less likely to be damaged by soil freezing.
0