North Skunk River IA 03-NSK-859
from the Mahaska/Poweshiek line to confluence with Sugar Cr. in S20 T78N R16W Poweshiek Co.
- Cycle
- 2018
- Release Status
- Final
- Overall IR
- 5 - Water is impaired or threatened and a TMDL is needed.
- Trend
- Unknown
- Created
- 5/14/2019 9:24:05 AM
- Updated
- 8/2/2019 9:17:58 AM
The presumptive Class A1 (primary contact recreation) uses remain "not assessed" due to the lack of information upon which to base an assessment. The Class B(WW2) aquatic life uses are assessed (evaluated) as "partially supported" based on results of DNR/SHL biological sampling in 2001 and 2012.
The Class B(WW2) aquatic life uses are assessed (evaluated) as “partially supporting” based on data collected in 2001 and 2012 as part of the DNR/SHL stream biocriteria project. A series of biological metrics which 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 that were 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 2001 FIBI score was 15 (poor) and the BMIBI score was 74 (good). The 2012 FIBI score was 14 (poor) and the BMIBI score was 42 (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 for previous Section 305(b) reports. The biological impairment criteria were determined from a statistical analysis of data collected at stream ecoregion reference sites from 1994-2008. The FIBI BIC for this ecoregion is 36 and the BMIBI BIC for this ecoregion is 51. This segment passed the FIBI BIC 0/2 times and passed the BMIBI BIC 1/2 times in the last 16 years. This aquatic life assessment is considered "evaluated" because there were not two or more samples collected from this segment in multiple years from over a recent five-year period. 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-t and remains on Iowa’s Section 303(d) list of impaired waters.