Indian Creek IA 02-CED-1875

Assessment Comments

Assessment is based on 2000 IDNR/UHL biological monitoring data: FIBI = 44 (fair), BMIBI = 79 (excellent) and on 1998 IDNR Fisheries data: FIBI = 50 (fair). Non-riffle habitat FIBI BIC = 44, natural substrate BMIBI BIC = 70.

Basis for Assessment

Note:  Prior to the 2008 Section 305(b) cycle, this stream segment was classified only for general 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 and for Class B(WW1) aquatic life uses.   According to the Iowa Water Quality Standards, all perennial rivers and streams and all intermittent streams with perennial pools that are not specifically listed in the Iowa surface water classification are designated as Class A1 and Class B(WW1) waters.   Thus, for the current (2010) assessment, perennial flow is presumed, and the available water quality monitoring data will be compared to the applicable Class A1 and Class B(WW1) 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 presumptive Class B(WW-1) aquatic life uses are assessed (evaluated) as "fully supported" based on results of IDNR/UHL biological (biocriteria) sampling in 2000 and IDNR Fisheries sampling in 1998.   The 1998 and 2000 sampling data are now greater than five years old; therefore, this aquatic life use assessment is now considered "evaluated" instead of "monitored".  

EXPLANATION:  The assessment of aquatic life uses was based on data collected in 1998 and 2000 as part of the IDNR/UHL stream biocriteria and IDNR Fisheries sampling projects.   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 1998 Fisheries FIBI score was 50 (fair).   The 2000 FIBI score was 44 (fair) and the BMIBI score was 79 (excellent).   The aquatic life use support was assessed (evaluated) as fully supported (=FS), based on a comparison of the FIBI and BMIBI scores with biological impairment criteria (BIC) established 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 natural substrate BMIBI BIC for this ecoregion is 70.   This segment passed the FIBI BIC 2/2 times in the last 11 years and passed the BMIBI BIC 1/1 times in 2000.   Even though this site passed both the FIBI and BMIBI BICs, it is uncertain as to whether or not this segment is meeting the aquatic life criteria because it is a small general use stream and doesn’t fall in the calibrated watershed size.

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 FIBI samples collected in the previous 11 years (1998-2008); however, the multiple 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).    Despite this change in assessment methodology and type, this waterbody remains in IR Category (2a) 5b and remains on Iowa’s 2010 Section 303(d) list of impaired waters.