Crooked Creek IA 03-SKU-918

Assessment Comments

Assessment remains based on 2005 IDNR/UHL biological monitoring data: FIBI = 39 (fair), BMIBI = 59 (good). FIBI BIC = 36; BMIBI BIC = 51.

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/EXPLANATION:  The presumptive Class A1 (primary contact recreation) uses are "not assessed" due to the lack of information upon which to base an assessment.  

The assessment of the Class B(WW2) aquatic life uses remains based on data collected in 2005 as part of the IDNR/UHL stream REMAP 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 2005 FIBI score was 39 (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 FIBI BIC for this ecoregion is 36 and the BMIBI BIC for this ecoregion is 51.   The biological impairment criteria were determined from a statistical analysis of data collected at stream ecoregion reference sites from 1994-2004.

This aquatic life assessment is considered "evaluated" because there were not two or more samples collected from this segment in multiple years from 2004-2008.   However, despite this change in assessment methodology and type, this waterbody remains in IR 2a.