Assessment Comments
Assessment is based on results of IDNR/UHL biocriteria sampling in 2001.
Basis for Assessment
SUMMARY: The Class B(LR) aquatic life uses remain assessed (monitored) as "partially supported" based on results of IDNR/UHL biological (biocriteria) monitoring in 2001. No cause or source of this impairment was identified. This assessment is the same as that developed for the 2002 reporting cycle.
EXPLANATION: This assessment is based on data collected in 2001 as part of the DNR/UHL stream biocriteria project. A series of biological metrics which reflect stream water quality and habitat integrity were calculated from the biocriteria sampling data. The biological metrics are based on the numbers and types of benthic macroinvertebrate taxa and fish species that were collected in the stream sampling reach. The biological metrics were combined to make a fish community index of biotic integrity (F-IBI) and a benthic macroinvertebrate index (BM-IBI). The indexes rank the biological integrity of a stream sampling reach on a rising scale from 0 (minimum) to 100 (maximum). The 2001 Fish IBI score was 69 (good) and the BM-IBI score was 43 (fair). The aquatic life use support was assessed as partially supporting (=PS), based on a comparison of the F-IBI and BM-IBI scores with biological assessment criteria established specifically for the 2002 Section 305(b) report. The biological assessment criteria were determined from a statistical analysis of data collected at stream ecoregion reference sites from 1994-2001.
Previous assessments of impairment were based on the occurrence of two fish kills in 1997 (see assessments developed for the 1998 and 2000 reports for more information). According to IDNR's assessment methodology for Section 305(b) reporting, the lack of a pollution-caused fish kill within the most recent three-year period indicates that any fish kill-related impacts have likely dissipated. Thus, the lack of recent fish kills in this stream segment suggests that previous (1997) fish kills are no longer directly causing impairment.
