Iowa DNR

Water Quality Assessments

Impaired Waters List

Prairie Creek IA 03-SSK-6598

from mouth (SE1/4 S34 T85N R25W) to headwaters in the NW1/4 S33 T85N R26W.

Assessment Cycle
Release Status
Cycle Period
2014 - 2016
Overall IR Category
5 - Water is impaired or threatened and a TMDL is needed.
7/19/2019 7:24:41 AM
7/19/2019 7:25:26 AM
Assessment conducted in accordance with Iowa's 2018 IR methodology
Use Support
Class A1
Not Supported
Bacteria: Indicator Bacteria- E. coli
Support Level
Not Supported
Impairment Code
5p - Impairment occurs on a waterbody with a presumptive A1 or B(WW1) use.
Cause Magnitude
Unknown: Source Unknown
Source Confidence
Cycle Added
Impairment Rationale
Geometric mean criterion exceeded
Data Source
Volunteer monitoring
TMDL Priority
Tier III
Class BWW1
Not Assessed
General Use
Not Assessed
Impairment Delistings
No delistings for this assessment cycle.
Assessment Summary

The presumptive Class A1 (primary contact recreation) uses remain assessed as “not supporting” due to levels of indicator bacteria that far exceed Iowa water quality criteria.  The presumptive Class B(WW1) aquatic life uses remain “not assessed” due to lack of information upon which to base an assessment.  The source of data for this assessment remains the results of monitoring at Iowa DNR monitoring station SC-13 (STORET station 908022) conducted as part of Iowa DNR water quality snapshot monitoring from 2008 through 2012. Additionally, because these data are now considered too old (greater than five years) to accurately characterize current water quality conditions, the assessment categories are considered “evaluated” (indicating an assessment with relatively lower confidence) as opposed to "monitored" (indicating an assessment with relatively higher confidence).  

Assessment Explanation

The Class A1 (primary contact recreation) remain assessed as "not supported" based on levels of indicator bacteria that exceeded state water quality criteria. The geometric mean of indicator bacteria (E. coli) in the nine samples collected during the recreational seasons of 2008 through 2012 at station SC-13 was 1,070 orgs/100 ml, thus far exceeding the Class A1 criterion of 126 orgs/100 ml. All nine of the samples (100%) exceeded the Class A1 single-sample maximum criterion of 235 orgs/100 ml. According to U.S. EPA guidelines for Section 305(b) reporting and DNR’s assessment/listing methodology, if a the geometric mean of at least 10 samples collected over five years of snapshot monitoring exceeds the respective water quality criterion, the contact recreation uses should be assessed as "impaired". Although only nine samples were collected over the five-year period, the relatively high geometric mean and the occurrence of greater than the single-sample maximum criterion (235 orgs/100 ml) in all nine samples suggests that the presumptive Class A1 uses should be assessed as "not supporting" (impaired).

None of the other parameters collected at this station over the 2008-2012 period have Class B(WW1) water quality criteria to which monitoring results can be compared. Thus, the presumptive Class B(WW1) aquatic life uses of this segment remain "not assessed".

Monitoring and Methods
Assessment Key Dates
5/10/2008 Fixed Monitoring Start Date
5/12/2012 Fixed Monitoring End Date
420 Water column surveys (e.g. fecal coliform)
830 (VOL.) Bacteriological water column sampling by quality-assured volunteers
150 Monitoring data more than 5 years old