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Monitoring Summer E. Coli Bacteria Levels in Iowa Lakes

Escherichia coli (E. coli) bacteria normally live in the environment, foods, and in the intestines of healthy people and animals. Most types of E. coli are harmless or have minor symptoms, but a few strains can cause more serious problems. People can be exposed to E. coli from contaminated water or food. Bacteria, and other pathogens, are carried into the water by fecal contamination, which can occur from septic systems, sewage treatment plants, storm water runoff, manure spills, or from animals or small children in the water.  

The bacteria standard for Iowa’s recreational waters consists of two components:

  • A one-time maximum based on a single sample - 235 colony forming units (CFU) of E. coli bacteria per 100 mL of water.
  • A geometric mean based on 5 samples in a 30-day period - 126 colony-forming units (CFU) of E. coli bacteria per 100 mL of water.

If either number exceeds these levels, the beaches remain open, but signs are posted.

George Wyth State Park, Waterloo, IA

Driving Question

  • How can we reduce the number of days there are water quality warnings for George Wyth Lake or at other lakes?

Probing Questions

  • How is the E. coli bacteria getting into the water?
  • What are some possible explanations for the changing levels of E. coli bacteria in the lake during the summer months?
  • How does the data from the two different state parks compare? Identify patterns, similarities and differences in the data.
  • How dangerous is it to swim in lakes with high E. coli levels?
  • What are possible ways to reduce the E. coli levels in the future?

Classroom Suggestions

Students could:

  • Study the characteristics of bacteria as an organism and what it needs to survive and thrive.
  • Look at some of the other factors (i.e. temperature, dissolved oxygen, etc.) from the water testing data and determine possible connections, correlation, causation, etc.
  • Look at the topographic or satellite maps of the parks and surrounding areas. Compare the hydrologic cycle and geography from the two state parks. 

Relevant Related Resources

Iowa Core Alignment


Apply scientific principles to design a method for monitoring and minimizing a human impact on the environment

Credit Info

Submitted by Tony DiLeo as part of his Iowa STEM Teacher Externship program.

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