ADBNet

Assessment Comments

Assessment based on 1996, 2002 and 2007 IDNR/SHL biological sampling data (CBI = 56, 64 and 76; CW BIC = 60) and on a 2012 summary of trout reproduction in Iowa streams prepared by the IDNR Fisheries Bureau.

Basis for Assessment

[Note:  Prior to the 2008 Section 305(b) cycle, this stream segment was designated only for Class B(CW) 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 also now presumptively designated for Class A1 (primary contact recreation) and Class A2 (secondary contact recreation) uses.   This segment remains designated for coldwater aquatic life use (now termed Class B(CW1) uses), and for fish consumption uses (now termed Class HH (human health/fish consumption) uses.]

SUMMARY:  The presumptive Class A1 (primary contact recreation) uses and the presumptive Class A2 (secondary contact recreation) uses remain "not assessed" (IR 3a) due to the lack of information upon which to base an assessment.   The Class B(CW1) coldwater aquatic life uses are assessed (evaluated) as "fully supported" (IR 2a).   Fish consumption uses remain "not assessed" (IR 3a).   The sources of data for this assessment are (1) results of IDNR/SHL biological sampling in 1996, 2002 and 2007 and (2) results of an IDNR Fisheries Bureau summary of trout reproduction in Iowa’s coldwater streams.  

EXPLANATION:  The assessment of the Class B(CW1) aquatic life uses was based on data collected in 1996, 2002 and 2007 as part of the IDNR/SHL coldwater stream sampling project.   A series of biological metrics which reflect coldwater stream water quality and habitat integrity were calculated from the biological sampling data.   The biological metrics are based on the numbers and types of benthic macroinvertebrate taxa that were collected in the stream sampling reach.   The biological metrics were combined to make a coldwater benthic index (CBI).   The index ranks the biological integrity of a coldwater stream sampling reach on a rising scale from 0 (minimum) to 100 (maximum).   The 1996 CBI score was 76, the 2002 CBI score was 56 and the 2007 CBI score was 64.  The aquatic life use support was assessed (evaluated) as fully supporting (=FS), based on a comparison of the CBI scores with biological impairment criteria (BIC) established for the 2012 Section 305(b) report.  The biological impairment criteria were determined from a statistical analysis of data collected at coldwater stream reference sites from 1994-2011.  The CW BIC is 60 and this segment passed the CW BIC 2/3 times in a a 17 year period.  

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 over a five-year period to be considered “monitored”.   This segment had multiple samples collected in a 17 year period (1996-2012); however, the multiple samples were not collected during a five-year period.   Additionally, all of the biological sampling data are greater than five years old.   Despite this change in assessment methodology and type, this waterbody remains in IR Category 2a.  

In addition, based on an updated summary of trout reproduction in Iowa streams prepared by the IDNR Fisheries Bureau in February 2012, the Class B(CW1) uses are assessed as "fully supported".   According to the updated summary, Smith Creek (aka Trout River) is in the group of Iowa coldwater streams that supports natural reproduction of trout.   Based on results of surveys by the IDNR Fisheries Bureau, this stream is placed in the category of Iowa trout streams that exhibit fairly consistent natural reproduction and maintain a viable population of brown trout without any stocking and exhibits some natural reproduction of rainbow trout.

Fish consumption uses remain "not assessed" due to lack of fish tissue monitoring in this stream reach.