Elk Creek IA 02-SHL-798

[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.]

The assessment was based on data collected in 2008 and 2012 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 2008 FIBI score was 47 (fair) and the BMIBI score was 27 (poor). The 2012 FIBI score was 10 (poor) and the BMIBI score was 17 (poor). The aquatic life use support was assessed as partially supporting (=PS), 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. The non-riffle habitat FIBI BIC for this ecoregion is 32 and the BMIBI BIC for this ecoregion is 62. This segment passed the FIBI BIC 1/2 times and passed the BMIBI BIC 0/2 times in the past seven years (2008-2014).

Because of the segment's proximity to the upstream marsh, and the marsh-like qualities of the year site, it was determined to loosely apply the biological criteria and enter this assessment as evaluated. According to IDNR's assessment methodology, "evaluated" impairments are of relatively lower confidence than “monitored" impairments which have relatively higher confidence. Such "evaluated" waters, while not appropriate for addition to Category 5 of the Integrated Report (= Section 303(d) list), will be placed in either Category 2b or 3b of the IR and thus will be added to the state’s list of “waters in need of further investigation”.

This aquatic life assessment is now also 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 2010 and 2014 to be considered “monitored”. This segment had multiple samples collected in the previous sevev years (2008-2014). According to IDNR’s assessment/listing methodology, impairments based on “evaluated” assessments are of lesser confidence and are thus not appropriate for Section 303(d) listing (Category 5 of the Integrated Report). IDNR does, however, consider these impairments as appropriate for listing under either Category 2b or 3b of the Integrated Report (waters potentially impaired and in need of further investigation).