Coldwater Creek IA 02-SHL-789

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: FIBI = 42 (fair), BMIBI = 59 (good). Non-riffle habitat FIBI BIC = 44, artificial substrate BMIBI BIC = 52.

Basis for Assessment

[Note:  Prior to the current (2008) Section 305(b) cycle, this stream segment was designated only for Class B(LR) aquatic life uses.   Due to changes in Iowa’s surface water classification that were approved by U.S.  EPA in February 2008 (see http://www.iowadnr.com/water/standards/files/06mar_swc.pdf), this segment is now presumptively designated for Class A1 (primary contact recreation) uses.   The stream remains designated for aquatic life uses (now termed Class B(WW2) aquatic life uses).   Thus, for the current (2008) assessment, the available water quality monitoring data will be compared to the applicable Class A1 and Class B(WW2) water quality criteria.]

SUMMARY:  The presumptive Class A1 (primary contact recreation) uses are "not assessed" due to the lack of information upon which to base an assessment.   The Class B(WW2) aquatic life uses are assessed (monitored) as “fully supported” based on results of IDNR/UHL biological monitoring conducted in 2002 as part of the stream biocriteria project.   Sources of data for this assessment include (1) results of IDNR/UHL biological monitoring conducted in August 2002 as part of the stream biocriteria project and (2) report of a fish kill that occurred on July 12, 2002.  

EXPLANATION: The assessment of the Class B(WW2) aquatic life uses was based on biological data collected in August 2002 as part of the DNR/UHL stream biocriteria project.   The 2002 FIBI score was 42 (fair) and the BMIBI score was 59 (good).   The aquatic life use support was assessed as Fully Supporting (=FS), based on a comparison of the FIBI and BMIBI scores with biological impairment criteria (BIC) established for previous Section 305(b) reports.  The biological impairment criteria were determined from a statistical analysis of data collected at stream ecoregion reference sites from 1994-2004.   The non-riffle habitat FIBI BIC for this ecoregion is 44 and the artificial substrate BMIBI BIC for this ecoregion is 52.

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.   However, the biological sampling was conducted in the same segment following the fishkill and the results indicated "full support" of aquatic life uses.