Elkhorn Creek IA 05-NSH-1901

Assessment Comments

Assessment remains based on 2002 Fisheries data: average FIBI (n=2) = 45 (fair). FIBI BIC = 31.

Basis for Assessment

[Note:  Prior to the current (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 (2008) 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/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 presumptive Class B(WW1) aquatic life uses remains based on data collected in 2002 as part of a DNR Fisheries stream sampling project: Cold Springs Fish Management.   A series of biological metrics which reflect stream water quality and habitat integrity were calculated from the Fisheries sampling data.   The biological metrics are based on the numbers and types 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).   The index ranks the biological integrity of a stream sampling reach on a rising scale from 0 (minimum) to 100 (maximum).   The 2002 evaluated average FIBI (n=2) was 45 (fair).   The aquatic life use support was assessed (evaluated) as Fully Supporting (=FS), based on a comparison of the average FIBI score 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 1994-2004.   The FIBI BIC for this ecoregion is 31.