North Cedar Creek IA 01-YEL-431

The assessment of the Class B(CW1) aquatic life uses was based on data collected in 2011 and 2014 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 2011 score was 63 and the 2014 score was 51.  The aquatic life use support was assessed (monitored) 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 1/2 times in a four year period (2011-2014).  IDNR normally requires a segment to have a simple majority of passing scores from multiple years in a five-year period to be considered fully supporting (monitored).  However, this assessment of North Cedar Creek includes the professional judgment of IDNR staff incorporating an in-depth analysis of the metric scores, sampling conditions and the fish sampling that occurred at the time the benthic macroinvertebrates were sampled.  Additionally, the fish sampling conducted at this segment combined with the natural reproduction data (see below) indicate a healthy trout population in this segment.  

In addition, the B(CW1) aquatic life assessment was based on an updated summary of trout reproduction in Iowa streams prepared by the IDNR Fisheries Bureau in January 2016, the Class B(CW1) uses are assessed as "fully supported".  According to the updated summary, North Cedar 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 of brook and brown trout at this time (a Category II stream).  This assessment is consistent with previous assessments of the ability of this stream to support natural reproduction of trout. 
 
The results of the chemical monitoring conducted on this stream segment in from 2000 through 2001 as part of the Sny Magill Creek Non-point Source Project also suggest "full support" of the Class B(CW1) uses.  No violations of Class B(CW1) water quality criteria for dissolved oxygen or temperature occurred in the approximately 90 samples analyzed during this period.  All these data, however, have aged well beyond the ten-year period during which water quality data is considered able to characterize current water quality conditions.  Thus, the results of the monitoring from 1999-2001 may have little relevance to current water quality conditions in this assessment segment.

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