Coon Creek IA 01-UIA-265

The Class A1 (primary contact recreation) uses and the Class A2 (secondary contact recreation) uses are both assessed as "not supported" based on levels of indicator bacteria that exceeded state water quality criteria.  The geometric means of indicator bacteria (E. coli) in the 21 samples collected during the recreational seasons of 2012 through 2014 at UIRW Site 19 were as follows:  the 2012 geometric mean was 932 orgs/100 ml, the 2013 geometric mean was 866 orgs/100 ml and the 2012 geometric mean was 816 orgs/100 ml.  All three geometric means exceed the Class A1 criterion of 126 orgs/100 ml, and all three geometric means also exceed the Class A2 criterion of 630 orgs/100 ml.  Sixteen of the 21 samples (76%) exceeded the Class A1 single-sample maximum criterion of 235 orgs/100 ml; four of the 21 samples (24%) exceeded the Class A2 single-sample maximum criterion of 2,880 orgs/100 ml.  According to U.S. EPA guidelines for Section 305(b) reporting and IDNR’s assessment/listing methodology, if a recreation season geometric mean exceeds the respective water quality criterion, the contact recreation uses should be assessed as “impaired” (see pgs 3-33 to 3-35 of U.S. EPA 1997b). 

The Class B(CW1) coldwater aquatic life uses are now considered “not assessed” based on the 1999 biological data due to the data age (greater than 10 years) upon which previous assessments (“fully supporting”) were based.  In past IR cycles, the assessment of the Class B(CW1) aquatic life uses was based on data collected in 1999 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 1999 CBI score was 54.  The aquatic life use support was assessed (evaluated) as fully supporting (=FS), 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 1/1 times in 1999.  This segment passed the CBI using the eight CW UAV (uncertainty adjustment value) applied to single sample assessments.  Additional biological monitoring is needed to update the aquatic life assessment for this stream segment. 

An updated summary of trout reproduction in Iowa streams prepared by the IDNR Fisheries Bureau in January 2016 suggests that the Class B(CW1) uses should be assessed as "fully supported".  According to the updated summary, Coon Creek 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 recent, but inconsistent reproductive success and that are generally not capable of maintaining a viable population for brown trout at this time (Category II stream).  This assessment is consistent with previous assessments of the ability of this stream to support natural reproduction of trout. 

Monitoring from 2012 to 2014 at Upper Iowa River Watershed Site 19 also suggests full support of the Class B(CW1) aquatic life uses.  This monitoring included analysis for ammonia, pH, and temperature.  Of the 14 samples analyzed for ammonia, 12 samples contained less than the limit of detection (0.05 mg/l); the two detected samples contained 1.6 and 0.09 mg/l of ammonia.  Although elevated, the concentration of 1.6 mg/l of ammonia is below the temperature/pH-dependent chronic ammonia criterion of 2.8 mg/l.  Thus, all levels of ammonia were below any Class B(CW1) aquatic life criteria for ammonia.  In addition, there were no violations of the Class B(CW1) criteria for pH or temperature in the 14 samples analyzed.  These results do not suggest impairment of the Class B(CW1) aquatic life uses. 

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