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Biological Monitoring​

During the first phase of the MPCA watershed approach – intensive watershed monitoring – the MPCA collected data about biology such as fish populations, chemistry such as pollutant levels, and flow to determine if lakes and streams were meeting water quality standards designed to ensure that waters are fishable and swimmable. Waters are “impaired” if they fail to meet standards. Researchers assessed the health of the watershed in 2008 and returned in 2018/2019 to conduct similar studies and assess the current health of the watershed.

Highlights of Monitoring

While individual streams in the watershed may have improved or declined in biological condition between 2008 and 2019, the overall health of macroinvertebrate (bug) communities showed little change and fish communities showed a slight improvement. Scientists use a tool called the Index of Biological Integrity (IBI) to assess the biological condition of aquatic communities. High IBI scores indicate a healthy community of fish or macroinvertebrates, and a healthy community indicates that water quality, habitat, and hydrology have not been impacted by human activities.


  • Across the Le Sueur Watershed, scientists captured a total of 41 fish species in four lakes during fish IBI sampling. Five of these species are considered intolerant to human stressors within the watershed, indicating good water quality, while six species were considered to be tolerant to these stressors, indicating poor water quality.

  • Elevated flows hampered fish sampling efforts in 2018. Fourteen of 44 stream stations were not sampled for fish. Sampling at these locations had to be postponed until 2019 due to persistent high flows. Flows had stabilized enough by August 2018 to allow for nearly every station to be sampled for macroinvertebrates.

  • Data from 2018 show that conditions improved for the fish community was previously impaired and now supports the standard, and for macroinvertebrate communities were considered impaired and conditions now support the standard.

  • Madison and St. Olaf are part of the Sentinel Lakes Program. The Sentinel Lakes Program is an intensive, long-term lake ecosystem monitoring program created to detect and understand the physical, chemical and biological changes occurring in Minnesota's lakes.

  • Scientists observed improving clarity at one station on the Little Cobb River (Bull Run Creek to Cobb River).

(Source:Le Sueur River Watershed Assessment and Trends Update (MPCA)

Learn More

Le Sueur River Watershed Assessment and Trends Update (MPCA)

Le Sueur River Watershed Monitoring and Assessment Report (MPCA)

Assessment of Selected Lakes within the Le Sueur River Watershed (Blue Earth, Waseca, Faribault, Steele, Freeborn Counties) (MPCA)

Le Sueur River Watershed Biotic Stressor Identification Report (MPCA)

Summary, Identifying conditions stressing fish and macroinvertebrates, Le Sueur River Watershed (MPCA)

Biological Monitoring – Fish Sampling (MPCA)

Biological Monitoring – Invertebrate Sampling (MPCA)

Electrofishing with the MPCA (MPCA)

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