Crane Creek IA 01-TRK-212

Assessment Comments

Assessment is based on 1994 and 2000 IDNR/UHL biological monitoring data: FIBI = 70, 64 (good), BMIBI = 78 (excellent), 56 (good). Non-riffle habitat FIBI BIC = 44; artificial substrate BMIBI BIC = 52, natural substrate BMIBI BIC = 70.

Basis for Assessment

[Note:  Prior to the 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 (2010) 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 remain "not assessed" due to the lack of information upon which to base an assessment.   The Class B(WW-2) aquatic life uses remain assessed (evaluated) as "fully supported"  based on results of IDNR/UHL biological (biocriteria) sampling in 1994 and 2000.  

EXPLANATION:  This evaluated aquatic life assessment was based on data collected in 1994 and 2000 as part of the IDNR/UHL stream biocriteria project.   A series of biological metrics which reflect stream water quality and habitat integrity were calculated from the biological sampling data.   The biological metrics are based on the numbers and types of benthic macroinvertebrate taxa and fish species collected in the stream sampling reach.   The biological metrics were combined to make a fish community index of biotic integrity (FIBI) and a benthic macroinvertebrate index (BMIBI).   The indexes rank the biological integrity of a stream sampling reach on a rising scale from 0 (minimum) to 100 (maximum).   The 1994 FIBI score was 70 (good) and the BMIBI score was 78 (excellent).   The 2000 FIBI score was 64 (good) and the BMIBI score was 56 (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 non-riffle habitat FIBI BIC is 44 (both samples), the artificial substrate BMIBI BIC is 52 (2000 sample) and the natural substrate BMIBI BIC is 70 (1994 sample).   This segment passed the FIBI and BMIBI BICs 2/2 times in the last 15 years.   The biological impairment criteria were determined from a statistical analysis of biological data collected at stream ecoregion reference sites from 1994-2004.  

This aquatic life assessment is now considered "evaluated" based on a change in the 2010 IDNR assessment methodology.   IDNR now requires a segment have two or more biological samples collected from the segment in multiple years between 2004 and 2008 to be considered “monitored”.     This segment had multiple samples collected in the previous 15 years (1994-2008); however, the samples were not collected during 2004-2008.   Additionally, because these data are now considered too old (greater than five years) to accurately characterize current water quality conditions, the assessment category is considered “evaluated” (indicating an assessment with relatively lower confidence) as opposed to "monitored" (indicating an assessment with relatively higher confidence).   However, despite this change in assessment methodology and type, this waterbody remains in IR Category 2a.