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Impairments affecting Wisconsin waters

Monitoring and assessments

Impaired waters are identified by comparing monitoring results for a given water to water quality parameter thresholds which provide guidelines for identifying water quality condition. For example, managers identify attainment of Fish and Aquatic Life uses for a given stream is by reviewing the type, number, and presence of aquatic macroinvertebrate species and fish species. Field results are compared to expected values for biological measures including the Fish Index of Biological Integrity (FIBI) and the Macro– invertebrate Index of Biological Integrity (mIBI). The map below illustrates median mIBI values at all Wisconsin monitoring stations that were sampled for macroinvertebrates from 2002 to 2012. This map portrays over 2,000 median macroinvertebrate IBIs ("M–IBI") values for collected through monitoring between 2002 to 2012; the red values indicate an "M–IBI" value of "poor".

Wisconsin waters are treasures to be protected and enjoyed.
Wisconsin waters are treasures to be protected and enjoyed. DNR Photo

When one or both of the Fish IBI and Bug IBI values for a given stream consistently show poor values over time, the water is further evaluated to determine specific pollutants and the related impairments (degraded biological community, eutrophication, sedimentation in stream bottoms) related to the poor biological communities. Land surveys, instream habitat evaluations, and stream chemistry data are gathered to determine the specific pollutants and associated impairments for the stream or section of stream. This additional evaluation is necessary to differentiate ’natural conditions’, such as areas where background soil levels of total phosphorus affect nutrient levels in surface waters, from those where human actions affect water condition, such as eroding streambanks from grazing practices or intensive urban development affecting the volume, magnitude, velocity of stormwater water runoff.

The federal Clean Water Act (CWA) requires that states adopt water quality standards to protect waters from pollution. These standards set the water quality goals for a lake, river, or stream by stating the maximum amount of a pollutant that can be found in the water while still allowing it to be used for fishing, swimming, and allowing aquatic organisms and wildlife to thrive. Water quality standards are put into place with the use of criteria, or specific quantitative measurements of a pollutant or nutrient such as phosphorus, sediment (total susended solids), bacteria ( E.coli), polychlorinated biphenyls, and mercury. A water is polluted or "impaired" if it does not support full use by humans, wildlife, fish and other aquatic life and it is shown that one or more of the pollutant criteria are not met.

Last revised: Tuesday May 26 2015