Burr Oak Creek IA 02-CED-581

The assessment of the Class B(CW1) aquatic life uses was based on data collected in 2010, 2011 and 2013 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 2010 CBI score was 50, the 2011 CBI score was 63 and the 2013 CBI score was 47.   The aquatic life use support was assessed (monitored) as partially supporting (=PS), 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 1/3 times in a five-year period (2010-2014).   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.   This aquatic life assessment is now considered "monitored" 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 in a five-year period to be considered “monitored”.    This assessment used multiple samples collected in the previous five years (2010-2014).

Additionally, this assessment of Burr Oak Creek includes the professional judgment of IDNR staff incorporating an in-depth analysis of the metric scores, location of the stream (ecoregion) and the fish sampling that occurred at the time the benthic macroinvertebrates were sampled.   This segment is located in the 47c ecoregion while all of the CW reference sites are located in the 52b ecoregion.   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 contrast to the benthic macroinvertebrate sampling, 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 should be assessed as "fully supported".   According to the updated summary, Burr Oak 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 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.  

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