Assessment Comments
Assessment is based on 2003 and 2007 IDNR/UHL biological monitoring data: FIBI = 69 (good), BMIBI = 24 (poor), 48 (fair) and on 2004 IDNR Fisheries Bureau sampling: FIBI = 50 (fair).
Basis for Assessment
SUMMARY: The Class A1 (primary contact recreation) uses remain "not assessed" due to lack of information upon which to base an assessment. The Class B(WW1) aquatic life uses are assessed (evaluated) as "partially supported" based on results of IDNR/UHL biological monitoring in 2003 and 2007 IDNR Fisheries Bureau sampling in 2004. Fish consumption uses are "not assessed" due to lack of fish contaminant monitoring in this river segment.
EXPLANATION: The evaluated biological assessment of the Class B(WW1) aquatic life uses was based on data collected in 2003 and 2007 by IDNR/UHL and in 2004 by IDNR Fisheries Bureau. A series of biological metrics that reflect stream water quality and habitat integrity were calculated from the biocriteria sampling data. The biological metrics are based on the numbers and types of benthic macroinvertebrate taxa and fish species collected in the stream sampling reach. The biological metrics were combined to make a fish community index of biotic integrity (FIBI) and a benthic macroinvertebrate index (BMIBI). The indexes rank the biological integrity of a stream sampling reach on a rising scale from 0 (minimum) to 100 (maximum). The 2003 FIBI score was 69 (good) and the BMIBI score was 24 (poor). The 2007 BMIBI score was 48 (fair). The 2004 IDNR Fisheries FIBI score was 50 (fair). The aquatic life use support was assessed (evaluated) as partially supporting (=PS), based on a comparison of the FIBI and BMIBI scores with biological impairment criteria (BIC) established from a statistical analysis of data collected at stream ecoregion reference sites from 1994-2004. The riffle habitat FIBI BIC for this ecoregion is 65 and the artificial substrate BMIBI BIC for this ecoregion is 52. This segment passed the FIBI BIC 1/2 times and passed the BMIBI BIC 0/2 times in the last six years. This assessment is considered evaluated because the drainage areas (1195, 1219 and 1248 mi2) above these sampling sites are greater than the maximum limit (500 mi2) that was used to calibrate the Iowa wadeable stream impairment criteria. Even though this failed to meet the both the FIBI and BMIBI BICs, it is uncertain as to whether or not this segment is meeting the aquatic life criteria because it doesn’t fall in the calibrated watershed size.
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 between 2004 and 2008 to be considered “monitored”. This segment had multiple samples collected in the previous six years (2003-2008); however, the samples were not collected during 2004-2008. 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).
