Elk River IA 01-MAQ-9

Assessment Comments

Assessment remains based on 2007 IDNR/SHL biological sampling data: FIBI = 29 (fair); BMIBI = 50 (fair). 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, 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 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" (IR 3a) due to the lack of information upon which to base an assessment.   The Class B(WW2) aquatic life uses are assessed (evaluated) as "fully supported" (IR 2a) based on results of IDNR/SHL biological sampling in 2007.  

EXPLANATION: This evaluated aquatic life assessment was based on 2007 IDNR/SHL biological sampling data.   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 2007 FIBI score was 29 (fair) and the BMIBI score was 50 (fair).   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.   This segment met both BICs using the FIBI UAV of 7 points and the BMIBI UAV of 8 points.   The biological impairment criteria were determined from a statistical analysis of biological data collected at stream ecoregion reference sites from 1994-2008.  

This aquatic life assessment is considered "evaluated" because there were not two or more samples collected from this segment in multiple years during a five-year period.   This segment had a single sample collected in 2001.   Also, 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.