For the more information about the geologic resources of the National Park Service, please visit http://www.nature.nps.gov/geology/.


Water Level Changes in the Great Lakes

Decrease in lake levels on Lake Superior in Apostle Islands National Lakeshore (NPS photo).
Decrease in lake levels on Lake Superior in Apostle Islands National Lakeshore (NPS photo).

Water levels in the Great Lakes reflect a balance of water entering and leaving the system. The main components of this hydrologic balance include precipitation in the watershed that winds its way to the lakes (via streams, rivers, and groundwater), and loss of water through evapotranspiration and human uses.

The Great Lakes are currently experiencing a period of very low water levels through much of the system. Lake Superior, home to Apostle Islands National Seashore, had record low water in 2007 when the lake was 22 inches below full. Most climate models predict that Great Lakes water levels will drop further during the next century due to decreased precipitation and increased air temperature (and evaportranspiration). One study predicts that lake levels in Lake Michigan and Lake Huron may drop by as much as 4.5 ft (1.38 m) by 2090. Lower lake levels will have significant impacts on natural and cultural resources located near migrating shorelines, and adversely affect key park facilities, such as docks that are essential to recreational boating.


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Last Updated: August 15, 2011