Buck Creek IA 01-YEL-428

The assessment of the Class B(CW1) aquatic life uses was based on data collected in 2007, 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 2007 CBI score was 53, 2011 CBI score was 61 and the 2013 CBI score was 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 1/3 times in the last 10 years (2007-2016).

DNR 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 segment had two samples collected in a five year period; however, the data were inconclusive as to whether this segment was impaired so the assessment is still considered evaluated. The 2007 CBI score was used as the tiebreaker and those data are now greater than five years old. 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).

In contrast to the CBI results, an updated summary of trout reproduction in Iowa streams prepared by the DNR Fisheries Bureau in January 2019 suggests that the Class B(CW1) uses should be assessed as "fully supported". According to the updated summary, Buck Creek is in the group of Iowa coldwater streams that support 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 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).