Out One Lake and In Another – How long does it take water to flow through the Great Lakes?

Water that is in a lake does not stay in that lake. Where does the water go? If you think about the water cycle, you will be able to figure out several places that it might go. The length of time that it takes for the amount of water in a lake to be completly replaced (enter the lake) is called retention time. Each of the Great Lakes has a different retention time. Lake Superior’s retention time is much longer than the others: 194 years compared to just 75 years for Lake Huron, for example. Since the water mixes as it pours in and out, over the course of 194 years only half of the water in Lake Superior actually leaves.


When you have completed this activity you will be able to:

  • Construct an appropriate model of the water flow of the Great Lakes.
  • Define the concepts of retention time and replacement time and, describe how they are different.
  • Discuss how Lake Superior affects the dynamics of water flow, retention time and flushing rates for the Great Lakes system and why this is important

External Curriculum Materials


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