West Otter Creek IA 02-CED-516

Assessment Comments

Assessment based on 2001, 2010 and 2013 IDNR/SHL biological sampling data: FIBI = 79, 80 (excellent) and 61 (good), BMIBI = 77, 80, 86 (excellent). Riffle habitat FIBI BIC = 65 and 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, 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 remain "not assessed" (IR 3a) due to the lack of information upon which to base an assessment.   The Class B(WW-2) aquatic life uses are assessed (evaluated) as "fully supported"  based on results of IDNR/SHL biological (biocriteria) sampling in 2001, 2010 and 2013.

EXPLANATION:  The assessment of the Class B(WW-2) aquatic life uses was based on data collected in 2001, 2010 and 2013 as part of the IDNR/SHL stream biocriteria project.   A series of biological metrics which reflect stream water quality and habitat integrity were calculated from the biocriteria sampling data.   The biological metrics are based on the numbers and types of benthic macroinvertebrate taxa and fish species that were 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 2001 FIBI score was 79 (excellent) and the BMIBI score was 80 (excellent).   The 2010 FIBI score was 61 (good) and the BMIBI score was 86 (excellent).   The 2013 FIBI score was 80 (excellent) and the BMIBI score was 77 (excellent).   The aquatic life use support was assessed (evaluated) 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 1994-2008.   This segment passed the FIBI BIC 2/3 times and passed the BMIBI BIC 3/3 times in the last 13 years.   The riffle habitat FIBI BIC for this ecoregion is 65 and the natural substrate BMIBI BIC for this ecoregion is 70.  

This aquatic life assessment is considered "evaluated" because there were not two or more samples collected from this segment in multiple years over a five-year period that could complete the assessment.