Assessment Comments
Assessment based on (1) a pollutant-caused fish kill in July 2002 and (2) results of an IDNR/UHL biocriteria sampling in August 2002.
Basis for Assessment
SUMMARY: The Class B(LR) aquatic life uses are assessed (monitored) as “partially supported” based on occurrence of a fish kill in July 2002. Sources of data for this assessment include (1) results of IDNR/UHL biological monitoring conducted in 2002 as part of the stream biocriteria project and (2) report of a fish kill that occurred on July 12, 2002.
EXPLANATION: A fish kill occurred on in this stream segment on July 12, 2002. The kill affected 6 miles of this stream; an estimated 39,000 fish were killed. No cause was determined, but the investigator stated that the kill did not result from natural causes. According to IDNR's assessment methodology for Section 305(b) reporting, occurrence of a single pollution-caused fish kill within the most recent three-year period indicates ongoing impairment of the aquatic life uses. Results of biological monitoring, however, suggest that the aquatic life uses should be assessed (monitored) as “fully supported / threatened.” This assessment was based on biological data collected in 2002 as part of the DNR/UHL stream biocriteria project. This assessment was based on data collected in 2002 as part of the DNR/UHL stream biocriteria project. The 2002 Fish IBI score was 42 (fair) and the BM-IBI score was 61 (good). The aquatic life use support was assessed as fully supporting/threatened (=FS/T), based on a comparison of the F-IBI and BM-IBI scores with biological assessment criteria established for previous Section 305(b) reports. The biological assessment criteria were determined from a statistical analysis of data collected at stream ecoregion reference sites from 1994-2001. The biological assessment was conducted on August 12, 2002, one month following the July fish kill. Thus, the potential exists that the kill influenced results of the biological assessment.
