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The MPCA analyzes the chemistry of the water samples it collects in rivers and streams. But biological monitoring can often detect water quality problems that water chemistry analysis misses or underestimates. Chemical pollutants, agricultural runoff, hydrologic alterations such as stream bed alterations and damming, and other human activities have cumulative effects on biological communities over time. The condition of these communities represent the condition of their aquatic environment. The index of biological integrity serves as the basis for biological monitoring evaluations. The MPCA collaborates with local partners to select biological monitoring sites.

Elements of biological monitoring

Site selection

The MPCA samples at 300 to 400 sites in four to eight major watersheds each year; Minnesota's 80 watersheds are monitored on a 10-year rotation to track changes in water quality. The agency also has 60 fixed biological monitoring sites that were established in 2013 to track changes over time due to climate change. The sites are evenly divided across Minnesota’s ecoregions and stream types and were chosen due to their minimal or lack of stressors due to human activity. In addition, every five years, the agency randomly samples at 150 river and stream sites, also divided equally across the state’s ecoregions.

Monitoring work happens from May to September. Monitoring staff talk to landowners and then measure and mark off sections of rivers and streams, called "reaches," where they will do their work. The length of the reaches are calculated by multiplying 35 by the mean stream width; reaches range from 150 meters to 500 meters long.

Fish sampling

Evaluation of fish health typically includes:

  • taking fish samples. Staff use electrofishing and collect all fish, regardless of size, and identify and measure them and return them to the water.
  • a water chemistry sample. Monitoring crews collect water samples and the water is measured for temperature, pH, conductivity, dissolved oxygen, transparency, total suspended solids, phosphorus, nitrogen, and ammonia.
  • stream habitat assessment. Staff look at the in-stream and surrounding habitat, including land use, the shape of the stream channel and whether it's been altered, and more. Monitoring crews may conduct a general or a more detailed habitat survey.
  • a brief assessment of potential stream stressors. Staff looks for visible evidence of what may be causing harmful conditions.

Invertebrate sampling

Evaluating the health of macroinvertebrates (insects) includes:

  • taking macroinvertebrate samples. Staff collect samples of insect habitats in and around streams, including sediment from the stream bottom, aquatic plants, undercut stream banks, snags, and fallen leaves. The samples are brought to a lab so the bugs in them can be identified.
  • a water chemistry sample. Staff measure the water for temperature, pH, conductivity, dissolved oxygen, and transparency.
  • stream habitat assessment. Staff look at the in-stream and surrounding habitat, including land use, the shape of the stream channel and whether it's been altered, and more. Monitoring crews may conduct a general or a more detailed habitat survey.

Random survey of the nation's rivers and streams

Every five years, the MPCA contributes to national river and stream management efforts by collaborating with the U.S. EPA in a random survey of U.S. rivers and streams. The survey provides a broad context for our state river and stream monitoring work.

For this project, 150 sites were selected randomly and proportionally across Minnesota’s three ecoregions. In 2010, all station locations were newly established and sampled, whereas in 2015, 50% of the stations were newly established and 50% were pre-existing stations from the 2010 project. The pre-existing stations were used for trend analysis. Stations were sampled for biological communities of both fish and macroinvertebrates (bugs). Water chemistry samples were also collected and analyzed for various pollutants.

How does stream work differ between MPCA and DNR?

The MPCA's biological monitoring work may appear similar to work by the Department of Natural Resources, but there are distinct differences.

  • Assesses water quality
  • Uses fish and invertebrates as indicators of stream water quality
  • Conducts whole community stream fish surveys
  • Identify stream biological stressors
  • Manages game fish populations
  • Stocks fish
  • Stream restoration
  • Locates species of concern
  • Manages invasive species

Some DNR offices collect fish community data and share it with the MPCA. DNR completes monitoring for lake assessments based on fish and related stressor identification work.

Data and reporting

Detailed assessment information for individual streams can be found on the MPCA’s Environmental Data Access web page. To see the monitoring and assessment reports for specific Minnesota watersheds, see the Watershed web pages.