How Does Stratification Affect Water Quality?

Some lakes have water quality problems related to the layering of the lake’s waters, which occurs in the summer months. Because of its shallowness, Lake Erie is such a lake. During the summer, the warm surface layer of water does not mix with the colder bottom layer of water. If a lot of algae has grown in the lake, decay of the dead algae on the lake bottom may use up all of the oxygen in the cold bottom water layer. When there is no oxygen in the bottom waters, the water is said to be anoxic. Fish and other animals cannot live in these anoxic waters. In the fall, the surface water cools and mixes with the bottom water, resupplying the bottom water with oxygen needed for life.


  • Describe how stratification of lake waters influences water quality.
  • Explain how phosphorus affects oxygen levels in lakes.

External Curriculum Materials


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