Iowa DNR

Water Quality Assessments

Impaired Waters List

Little Sioux River IA 06-LSR-1578

from confluence with Milford Cr. (NW 1/4, S14, T98N, R37W, Dickinson Co.) to confluence with West Fork Little Sioux R. in S36, T100N, R38W, Dickinson Co.

Assessment Cycle
Release Status
Result Period
2002 - 2004
Class B(WW)
Assessment Type
Integrated Report
Category 3b
Legacy ADBCode
IA 06-LSR-0040_2
Overall Use Support
Aquatic Life Use Support
Fish Consumption
Not assessed
Assessment Comments

Assessment is based on results of IDNR/UHL: (1) ambient monthly monitoring near Milford from 2002-04 and (2) 2003 biocriteria data: FIBI = 31 (fair), BMIBI = 66 (good). Riffle FIBI BIC = 53; BMIBI BIC = 62.

Basis for Assessment

SUMMARY:  The Class B(WW) aquatic life uses are assessed (evaluated) as "partially supported” based on results of (1) biological monitoring in 2003 and (2) ambient chemical/physical water quality monitoring near Milford from 2002-04.   Fish consumption uses remain "not assessed" due to the lack of fish contaminant monitoring in this river segment.   This assessment is based on results of (1) IDNR/UHL biological (biocriteria) monitoring in 2003 and (2) IDNR/UHL monthly ambient monitoring conducted during the 2002-2004 assessment period near Milford (STORET station 10300001 (formerly station 920450)); this station is located approximately 1.2 miles west of Milford and is approximately 0.5 miles upstream from the confluence with Milford Creek.  

EXPLANATION:  The assessment was based on data collected in 2003 as part of the DNR/UHL stream biocriteria project.   The 2003 FIBI score was 31 (fair) and the BMIBI = 66 (good).   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 1994-2004.   The riffle site FIBI BIC for this ecoregion is 53 and the BMIBI BIC for this ecoregion is 62.   This assessment is considered evaluated because of the documented sampling problems encountered during the 2003 biological sampling.   Field staff rated the fish sampling quality as "fair" and listed depth, daylight limiting visibility, turbidity, width, and equipment malfunction as the reasons for the fair fish sampling quality.   Combining this knowledge with the fact that the BMIBI at this site passed the BMIBI BIC, there is reason to believe that with all the problems encountered during the fish sampling that the sample collected was not representative of the reach.   This site is a reference site and will be sampled in the near future.

Ambient chemical/physical water quality monitoring at the IDNR/UHL station near Milford showed no violations of Class B(WW) water quality criteria during the 2002-2004 assessment period for pH (range = 7.7 to 8.8 units) or ammonia-nitrogen (maximum value = 0.58 mg/l) in the 36 samples analyzed.   Levels of pesticides in the seven samples analyzed, and levels of toxic metals in the ten samples analyzed, were all below their respective Class B(WW) water quality criteria.   Monitoring results for dissolved oxygen, however, showed that one of the 36 samples analyzed (3%) violated the Class B(WW) water quality criterion for dissolved oxygen: the level of dissolved oxygen in the sample collected on February 9, 2004 (0.9 mg/l) was well below the Class B(WW) criterion of 5.0 mg/l.   According, however, to U.S.  EPA guidelines for Section 305(b) water quality assessments (U.S.  EPA 1997b, page 3-17), if 10% or less of samples exceed criteria for conventional parameters (e.g., dissolved oxygen and pH), aquatic life uses should be assessed as “fully supported”.   Over the five-year period since monthly monitoring was implemented at this IDNR/UHL station, levels of dissolved oxygen have occasionally violated the Class B(WW) criterion of 5.0 mg/l; usually these samples are collected in late winter or early spring.   In addition to the February 2004 sample, samples collected on January 9, 2001 and March 13, 2001 also violated the Class B(WW) criterion for dissolved oxygen.   While not indicating impairment of aquatic life uses, the magnitude and timing of these violations suggest some type of reoccurring condition, whether natural or man-made, that contribute to these violations.  

Fish consumption uses remain "not assessed" due to the lack of fish contaminant monitoring in this river segment.

Monitoring and Methods
Assessment Key Dates
12/13/2004 Fixed Monitoring End Date
7/22/2003 Biological Monitoring
1/15/2002 Fixed Monitoring Start Date
220 Non-fixed station physical/chemical monitoring (conventional pollutant only)
315 Regional reference site approach
320 Benthic macroinvertebrate surveys
330 Fish surveys
380 Quan. measurements of instream parms-- channel morphology-- floodplain-- 1-2 seasons-- by prof
230 Fixed station physical/chemical (conventional plus toxic pollutants)
Monitoring Levels
Biological 4
Habitat 4
Physical Chemistry 3
Toxic 3
Pathogen Indicators 0
Other Health Indicators 0
Other Aquatic Life Indicators 0
# of Bio Sites 1
BioIntegrity Good
Causes and Sources of Impairment
Causes Use Support Cause Magnitude Sources Source Magnitude
Organic enrichment/Low DO Aquatic Life Support Not Impairing
  • Source Unknown
  • Not Impairing