Iowa DNR

Water Quality Assessments

Impaired Waters List

Ioway Creek IA 03-SSK-954

mouth (S12 T83N R24W Story Co.) to confluence with unnamed tributary in NW 1/4 S9 T85N R25W Boone Co.

Assessment Cycle
Release Status
Data Collection Period
Overall IR Category
2 - Some of the designated uses are met but there is insufficient data to determine if remaining designated uses are met.
9/19/2016 10:24:57 AM
9/19/2016 10:24:57 AM
Assessment conducted in accordance with Iowa's 2016 IR methodology
Use Support
Class A1
Not Assessed
Class BWW2
Fully Supported
General Use
Not Assessed
Impairment Delistings
No delistings for this assessment cycle.
Assessment Summary

The presumptive Class A1 (primary contact recreation) uses remain "not assessed" (IR 3a) due to the lack of information upon which to base an assessment. The Class B(WW2) aquatic life uses remain assessed (evaluated) as "fully supported" (IR 2a) based on results of IDNR/SHL biological sampling in 2000 and 2002.

Assessment Explanation

[Note: Prior to the 2008 Section 305(b) cycle, this stream segment was designated only for Class B(LR) aquatic life uses. Due to changes in Iowa’s surface water classification that were approved by U.S. EPA in February 2008 (see, this segment is now presumptively designated for Class A1 (primary contact recreation) uses. The stream remains designated for aquatic life uses (now termed Class B(WW2) aquatic life uses). Thus, for the current assessment, the available water quality monitoring data will be compared to the applicable Class A1 and Class B(WW2) water quality criteria.]

The Class B(WW2) aquatic life uses remain assessed (evaluated) as “fully supporting” based on biological data collected in 2000 and 2002 as part of the IDNR/SHL stream biological sampling projects. 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 2000 FIBI scores were 41, 43 (fair) and 51 (good). The 2000 BMIBI scores were 74, 74 (good). The 2002 FIBI score was 45 (fair) and the BMIBI score was 80 (excellent). The aquatic life use support was assessed as fully supporting (=FS), 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 non-riffle habitat FIBI BIC for this ecoregion is 32 and the BMIBI BIC for this ecoregion is 62. This segment passed the FIBI BIC 4/4 times and passed the BMIBI BIC 3/3 times in the last 15 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 over a five-year period to be considered “monitored”. This segment had multiple samples collected in the previous 15 years (2000-2014); however, the multiple samples were not collected during a five-year period. Additionally, because these data are now considered too old (greater than five years) to accurately characterize current water quality conditions, the assessment category is considered “evaluated” (indicating an assessment with relatively lower confidence) as opposed to "monitored" (indicating an assessment with relatively higher confidence). Despite this change in assessment methodology and type, this waterbody remains in IR Category 2a.

Monitoring and Methods
Assessment Key Dates
7/12/2000 Biological Monitoring
7/13/2000 Biological Monitoring
7/14/2000 Biological Monitoring
7/18/2002 Biological Monitoring
150 Monitoring data more than 5 years old
315 Regional reference site approach
320 Benthic macroinvertebrate surveys
330 Fish surveys
380 Quantitative physical habitat assessment