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 DNR/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 seven-year period (2010-2016).

This aquatic life assessment is now considered "evaluated" based on a change in the 2010 DNR assessment methodology. DNR now requires a segment have two or more biological samples collected from the segment in multiple years in a recent five-year period to be considered “monitored”.This assessment used multiple samples collected in the previous seven years (2010-2016).According to DNR’s assessment/listing methodology, impairments based on “evaluated” assessments are of lesser confidence and are thus not appropriate for Section 303(d) listing (Category 5 of the Integrated Report). DNR does, however, consider these impairments as appropriate for listing under either Category 2b or 3b of the Integrated Report (waters potentially impaired and in need of further investigation). However, despite this change in assessment methodology and type, this waterbody remains in IR Category 5b-v and remains on Iowa’s 2018 Section 303(d) list of impaired waters.

Additionally, this assessment of Burr Oak Creek includes the professional judgment of DNR 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 DNR Fisheries Bureau in January 2019, 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 DNR Fisheries Bureau, this stream is placed in the category of Iowa trout streams that exhibit consistent natural reproduction and maintain a wild population of Brown Trout without any stocking (a Category I stream).

The Class A1 (primary contact recreation) uses, Class A2 (secondary contact recreation) uses and Class HH (fish consumption) uses remain "not assessed" due to the lack of information upon which to base an assessment.