Unnamed Tributary to Otter Creek IA 01-WPS-1909

Assessment Comments

Assessment based on 2004 IDNR/UHL stream REMAP data: FIBI = 43 (fair). Non-riffle habitat FIBI BIC = 44.

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:  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 aquatic life uses has changed between the 2006 and current (2008) Integrated Reports.   For the 2006 305(b) IR, this segment was reported to be "partially supporting" of the overall use designated use.   IDNR applied the incorrect FIBI BIC to this segment, and after further review, the site used to assess this segment was determined not to contain stable riffle habitat.   Thus, using the non-riffle habitat FIBI BIC, this segment met the non-riffle FIBI BIC using the Uncertainty Adjustment Value of seven points that is applied to single samples.


EXPLANATION:  The evaluated biological assessment of the presumptive Class B(WW1) aquatic life uses was based on data collected in 2004 as part of the DNR/UHL stream REMAP project.   A series of biological metrics that 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 fish species 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 2004 FIBI score was 43 (fair).  The aquatic life use support was assessed (evaluated) as Fully Supporting (=FS), based on a comparison of the FIBI score 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.   Even though this site met the FIBI BIC (using the FIBI UAV of 7 points), 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.