Assessment Comments
Assessment based on 2001 and 2007 IDNR/SHL biological sampling data (CBI = 41 and 44; CW BIC = 60) and on a 2012 summary of trout reproduction in Iowa streams prepared by the IDNR Fisheries Bureau.
Basis for Assessment
[Note: Prior to the 2008 Section 305(b) cycle, this stream segment was designated only for Class B(CW) aquatic life uses. Due to changes in Iowa’s surface water classification that were approved by U.S. EPA in February 2008, portions of this segment are also now presumptively designated for Class A1 (primary contact recreation), Class A2 (secondary contact recreation), and Class A3 (children’s recreation) uses. This segment remains designated for coldwater aquatic life use (now termed Class B(CW1) uses), and for fish consumption uses (now termed Class HH (human health/fish consumption) uses.]
SUMMARY: The presumptive Class A1 (primary contact recreation) uses, the presumptive Class A2 (secondary contact recreation) uses and the Class A3 (children’s recreation) uses remain "not assessed" due to the lack of data for indicator bacteria upon which to base an assessment (IR Category 3a). The Class B(CW1) aquatic life uses are assessed (evaluated) as "partially supported" (IR Category 3b-c) based on results of IDNR/SHL biological sampling in 2001 and 2007 and on an updated summary of trout reproduction in Iowa streams prepared by the DNR Fisheries Bureau in February 2012. Fish consumption uses remain "not assessed" (IR Category 3a).
EXPLANATION: The assessment of the Class B(CW1) aquatic life uses was based on data collected in 2001 and 2007 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 2001 CBI score was 41 and the 2007 CBI score was 44. The aquatic life use support was assessed (evaluated) 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 0/2 times in the last 10 years.
This aquatic life assessment is now considered "evaluated" 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 segment had multiple samples but they were not collected in a five-year period. Additionally, these data are now greater than five years old. According to IDNR’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). IDNR 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 benthic macroinvertebrate data, an updated summary of trout reproduction in Iowa streams prepared by the DNR Fisheries Bureau in February 2012, suggests the Class B(CW1) uses be assessed as "fully supported". According to the updated summary, Catfish 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 exhibit recent, but inconsistent, reproductive success and are not capable of maintaining a viable population of brown trout at this time. In addition, the natural reproduction segment is in the upper one mile of this 5.3 mile segment.
Fish consumption uses remain "not assessed" due to lack of fish tissue monitoring in this stream reach.
