Assessment Comments

Assessment based on (1) 2007, 2008 and 2010 IDNR/SHL biological sampling data and (2) occurrence of a fish kill in July 2002.

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, and due to completion and approval of a use attainability analysis, this segment is also now 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 Class A1 (primary contact recreation) uses and the Class A2 (secondary contact recreation) uses remain "not assessed" due to the lack of information upon which to base an assessment.   The Class B(CW1) aquatic life uses are assessed (monitored) as "partially supported" based on results of biological monitoring in 2007, 2008 and 2010 conducted as part of the IDNR/SHL stream biocriteria project.   Occurrence of a fish kill, possibly caused by runoff by land-applied manure, suggests an additional impairment of the aquatic life uses.   Fish consumption uses remain "not assessed" due to the lack of fish contaminant monitoring in this stream reach.  

EXPLANATION:  The assessment of the Class B(CW1) aquatic life uses was based on data collected in 2007, 2008 and 2010 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 2007 CBI score was 30.   The 2008 CBI scores were 37 and 37.   The 2010 CBI scores were 33, 37 and 43.   The aquatic life use support was assessed (evaluated) as partially supporting (=PS), based on a comparison of the CBI score 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 0/6 times in a four-year period (2007-2010).  

This aquatic life use assessment is considered "monitored" because there were two or more samples collected in multiple years from 2007-2010.  

In addition, a fish kill occurred on this stream on July 29, 2002.   The kill followed heavy rainfall following a long period of hot, dry weather.   No specific cause was determined, but runoff from feedlots and/or land applied manure is suspected due to presence of several feedlots in the watershed of this stream.   Approximately 0.5 mile of stream was affected, and 184 fish were killed.   According to IDNR's assessment methodology for Section 305(b) reporting, occurrence of a single pollution-caused fish kill indicates ongoing impairment of the aquatic life uses.   Any existing fish kill (5b) impairment will remain in IR Category 5b until more recent monitoring has shown full recovery from the kill event.   Thus, this assessment segment will remain in Category 5b of Iowa’s 2012 Integrated Report.  

Fish consumption uses remain "not assessed" due to the lack of fish contaminant monitoring in this stream segment.