Mill Creek (aka Big Mill Creek) IA 01-TRK-115
Alternate name(s) for this segment: Big Mill Creek
confluence with Little Mill Cr. to confluence with unnamed tributary in S1 T86N R3E Jackson Co.
- Cycle
- 2016
- Release Status
- Final
- Overall IR
- 3 - Insufficient data exist to determine whether any designated uses are met.
- Trend
- Unknown
- Created
- 8/23/2016 10:45:05 AM
- Updated
- 10/5/2016 7:23:54 AM
The presumptive Class A1 (primary contact recreation) uses and presumptive Class A2 (secondary contact 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) coldwater aquatic life uses are assessed (evaluated) as "partially supported" based on 2007 IDNR/SHL benthic macroinvertebrate sampling data and on the January 2016 summary of trout reproduction in Iowa streams as prepared by the IDNR Fisheries Bureau (IR Category 3b-c). Fish consumption (Class HH) uses remain "not assessed" (IR Category 3a).
The assessment of the Class B(CW1) aquatic life uses was based on data collected in 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 2007 CBI score was 34. 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 0/1 times in 2007.
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 over a five-year period to be considered “monitored”. This segment had a single sample collected in 2007. Additionally, the biological monitoring data are now greater than five years old. Despite this change in assessment methodology and type, this waterbody was placed in IR Category 3b-c.
In contrast to the benthic macroinvertebrate data, 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, (Big) Mill 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 have fairly consistent natural reproduction and that are capable of maintaining a viable population for the target trout species without any stocking (a Category I stream). This assessment is consistent with previous assessments of the ability of this stream to support natural reproduction of trout. However, the natural reproductive segment is only 1.5 miles of the total 8 mile segment.
Fish consumption uses remain "not assessed" due to lack of fish tissue monitoring in this stream reach.