Iowa DNR

Water Quality Assessments

Impaired Waters List

Little Sioux River IA 06-LSR-1565

from confluence with Maple R. (S17 T83N R44W Monona Co.) to confluence with Big Cr. in Anthon in S4 T87N R43W Woodbury Co.

Assessment Cycle
Release Status
Data Collection Period
Overall IR Category
5 - Water is impaired or threatened and a TMDL is needed.
5/30/2019 2:49:35 PM
7/30/2019 11:09:22 AM
Assessment conducted in accordance with Iowa's 2018 IR methodology
Use Support
Class A1
Partially Supported
Bacteria: Indicator Bacteria- E. coli
Support Level
Partially Supported
Impairment Code
5a - Pollutant-caused impairment. TMDL needed.
Cause Magnitude
Unknown: Source Unknown
Source Confidence
Cycle Added
Impairment Rationale
Geometric mean criterion exceeded
Data Source
Ambient monitoring: Iowa DNR-rivers
TMDL Priority
Tier III
Class BWW1
Fully Supported
Class HH
Not Assessed
General Use
Not Assessed
Impairment Delistings
No delistings for this assessment cycle.
Assessment Summary

The Class A1 (primary contact recreation) uses are assessed as "partially supported" due to levels of indicator bacteria that violate state water quality criteria. The Class B(WW1) aquatic life uses are assessed (evaluated) as "fully supported" based on 2012-2014 DNR/SHL stream biological sampling. Results of ambient water quality monitoring from 2014 through 2016 also suggest "full support" of the Class B(WW1) aquatic life uses. Fish consumption uses remain "not assessed" due to the lack of recent fish contaminant monitoring in this river segment. This assessment is based on results of (1) DNR/SHL monthly ambient monitoring conducted during the 2014-2016 assessment period NE of Smithland (STORET station 10970001) and (2) 2012-2014 DNR/SHL stream biological sampling near Smithland.

Assessment Explanation

The Class A1 (primary contact recreation) uses are assessed (monitored) as "partially supported" based on levels of indicator bacteria that exceeded state water quality criteria. The geometric means of indicator bacteria (E. coli) in the 24 samples collected during the recreational seasons of 2014 through 2016 at the Little Sioux River near Smithland (STORET station 10970001) were as follows: the 2014 geometric mean was 386 orgs/100 ml, the 2015 geometric mean was 335 orgs/100 ml, and the 2016 geometric mean was 480 orgs/100 ml. All three recreation season geometric means exceeded the Class A1 geometric mean criterion of 126 orgs/100 ml. Thirteen of the combined 24 samples (54%) exceeded Iowa’s 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 the geometric mean is greater than 126 orgs/100 ml., the primary contact recreation uses should be assessed as "impaired" (see pgs 3-33 to 3-35 of U.S. EPA 1997b). Thus, because at least one recreation season geometric mean exceeded criteria for Class A1 uses, these uses are assessed as "partially supported."

Regarding support of the Class B(WW1) aquatic life uses, the results of chemical/physical water quality monitoring at the Little Sioux River near Smithland (STORET station 10970001) suggest “full support” of the aquatic life uses. Monitoring showed no violations of Class B(WW1) water quality criteria for 36 Ammonia samples (maximum = 0.4 mg/L), 36 Dissolved Oxygen samples (minimum = 6.7 mg/L), 36 pH samples (range = 7.4 to 8.6), 36 Temperature samples (maximum = 24.9 °C), 36 Chloride samples (maximum = 32 mg/L), or 36 Sulfate samples (maximum = 150 mg/L) occurred during monitoring from January 2014 to December 2016. According to U.S. EPA guidelines for Section 305(b) water quality assessments (U.S. EPA 1997b, page 3-17), the EPA guidelines allow up to 10% violations of these conventional parameters before impairment of water quality is indicated. Thus, these results thus suggest “full support” of the Class B(WW1) aquatic life uses.

The results of the 2012-2014 DNR/SHL large river biological sampling near Smithland also suggest "full support" of the Class B(WW1) aquatic life uses. This evaluated biological assessment was based on data collected in 2012-2014 as part of the DNR/SHL REMAP and large river projects. 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 2012-2014 BMIBI scores were 54, 55 (all fair) and 68 (good). There were no FIBI/fish community samples collected in this reach in the last five years. The aquatic life use support was assessed (evaluated) as fully supporting (=FS), based on a comparison of the BMIBI scores with biological impairment criteria (BIC) established from a statistical analysis of data collected at stream ecoregion reference sites from 1994-2008. The BMIBI BIC for this ecoregion is 54. This assessment is considered evaluated because the drainage area (2687 mi2) above the sampling site was greater than the maximum limit (500 mi2) that was used to calibrate the Iowa wadeable stream impairment criteria. Even though this site passed the BMIBI BIC (3/3), it is uncertain as to whether or not this segment is meeting the aquatic life criteria because the sites used for the assessment don’t fall in the calibrated watershed size.

Monitoring and Methods
Assessment Key Dates
1/8/2014 Fixed Monitoring Start Date
12/7/2016 Fixed Monitoring End Date
10/3/2012 Biological Monitoring
7/30/2013 Biological Monitoring
8/8/2014 Biological Monitoring
230 Fixed station physical/chemical (conventional plus toxic pollutants)
315 Regional reference site approach
320 Benthic macroinvertebrate surveys
420 Indicator bacteria monitoring