Sustained Assessment of the Great Lakes

Overview of this Assessment

The Sustained Assessment of the Great Lakes is intended to be a continuous, sustained, community-based process to assess knowledge of GL ice cover, lake levels, hydrology, and climate. Lake levels and ice cover are basic, integrated measures important to lake and coastal ecosystems, coastal communities, and regional climate. They are influenced by accumulated heat and precipitation, cloudiness, wind, stream flow and lake circulation, and by human decisions on water and ice management. There is a substantial body of related knowledge; however, much of the local information required for decision making is not published in broadly accessible venues or has been generated in a relatively uncoordinated way.  This effort is meant to create the capability to more easily extract information for specific applications and support continuous evaluation of research priorities to address knowledge gaps.

General Information about the Great Lakes

The Great Lakes make up 84% of North America’s surface fresh water, with approximately 4,500 miles of coastline. Formed by glaciers during the last ice age, the lake system flows out into the Atlantic Ocean through the St. Lawrence Seaway. Lake Superior is the largest lake, when Lakes Michigan and Huron are considered separately, in terms of surface area and volume. Lake Erie is the smallest of the Great Lakes with the lowest volume. Because of the Georgian Bay and the Manitoulin Island (which is the largest freshwater lake island in the world), Lake Huron has the longest shoreline out of any of the lakes. Lakes Superior, Michigan, and Huron all have comparably sized drainage basins.

 Lake SuperiorLake MichiganLake HuronLake ErieLake Ontario
Surface Area (sq. miles)31,70022,30023,0009,9107,340
  Volume (cu. miles)2,9001,180850116393
  Shoreline (miles)2,7261,6593,827871712
Drainage Basin (sq. miles)49,30045,60051,70030,14024,720

The following is a color-coded map showing the overall drainage basin area and individual basins for each Great Lake. Major cities in the Great Lakes basin are also indicated.  Source: Environment and Climate Change Canada.

A profile view of the Great Lakes system showing the various lake depths and elevations is shown below. It also shows the man-made locks that have been constructed throughout the system. Water flows from left to right in this profile image, starting in Lake Superior, flowing down through Lake Ontario, and out through the St. Lawrence River.

GLISA would like to thank Drew Gronewold (, Associate Professor in the School for Environment and Sustainability at the University of Michigan, for his contribution to this Assessment.

If you have questions, comments, or feedback on the Sustained Assessment of the Great Lakes, please contact Kim Channell (