Iowa DNR

Water Quality Assessments

Impaired Waters List

Floyd River IA 06-FLO-1552

mouth to West Branch Floyd R. in S2, T91N, R46W, Plymouth Co.

Assessment Cycle
Release Status
Result Period
2000 - 2002
Assessment Type
Integrated Report
Category 5a
Legacy ADBCode
IA 06-FLO-0010_0
Overall Use Support
Not supporting
Aquatic Life Use Support
Not supporting
Fish Consumption
Not assessed
Assessment Comments

Assessment is based on results of IDNR/UHL ambient monthly water quality monitoring near James from 2000-02.

Basis for Assessment

SUMMARY:  The Class B(WW) aquatic life uses are assessed (monitored) as "not supported" due to violations of state water quality criteria for ammonia-nitrogen.   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 IDNR monthly (plus) ambient monitoring conducted during the 2000-2002 assessment period at the County Road C-70 bridge north of Sioux City (STORET station 10750001 (formerly station 950110)).  

EXPLANATION:  Monitoring at the IDNR monthly ambient monitoring station north of Sioux City showed no violations of Class B(WW) water quality criteria for pH in the 50 samples analyzed or for pesticides in the 17 samples analyzed during the 2000-2002 assessment period.   Levels of dissolved oxygen and ammonia-nitrogen, however, did violate the Class B(WW) criteria during the assessment period.   The sample collected on April 1, 2001, contained 4.7 mg/l of dissolved oxygen, thus violating the Class B(WW) criterion of 5.0 mg/l.   According to U.S.  EPA guidelines for Section 305(b) water quality assessments (U.S.  EPA 1997b, page 3-17), however, the percentage of violation for dissolved oxygen at this station (2%) does not suggest a water quality impairment.   These guidelines allow up to 10% violations of conventional parameters such as dissolved oxygen before impairment of water quality is indicated.   In addition, three of the 50 samples contained levels of ammonia nitrogen that exceeded state‚Äôs pH-dependent chronic water quality criteria for Class B(WW) waters  These violations occurred in samples collected on March 19, 2001, November 28, 2001, and July 11, 2002; these samples contained 1.2, 2.9, and 1.9 mg/l of ammonia-nitrogen, respectively.   According to U.S.  EPA guidelines for Section 305(b) reporting, if, for a dataset where at least 10 samples have been collected over a three-year period, more than one sample exceeds a criterion, impairment of aquatic life uses is indicated (see pg 3-18 of U.S.  EPA 1997b).   Based on IDNR modifications to the U.S.  EPA guidelines, the occurrence of more than one violation of a chronic criterion for a toxic parameter suggests that the aquatic life uses should be assessed as "not supported."  Data from this station suggest a period of relatively high levels of ammonia-nitrogen from early March through late April of 2001.   The levels of ammonia-nitrogen in the six samples collected during this period were as follows:  1.2 mg/l on March 6, 1.5 mg/l on March 19, 1.3 mg/l on March 28, 0.6 mg/l on April 3, 2.3 mg/l on April 12, and 0.8 mg/l on April 24.   Levels before and after this period were much lower (e.g., from <0.01 to 0.2 mg/l).   In addition, a plot of ammonia-nitrogen results from the IDNR/UHL station for the entire 2000-2002 period suggests typically very low levels of ammonia interspersed with spikes.   The high levels of ammonia-nitrogen seen in the Floyd River monitoring station are atypical for Iowa rivers, and their occurrence suggests a water quality problem in this river segment.  

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

Monitoring and Methods
Assessment Key Dates
12/18/2002 Fixed Monitoring End Date
1/1/2000 Fixed Monitoring Start Date
230 Fixed station physical/chemical (conventional plus toxic pollutants)
Monitoring Levels
Biological 0
Habitat 0
Physical Chemistry 3
Toxic 0
Pathogen Indicators 0
Other Health Indicators 0
Other Aquatic Life Indicators 0
# of Bio Sites 0
BioIntegrity N/A
Causes and Sources of Impairment
Causes Use Support Cause Magnitude Sources Source Magnitude
Unionized Ammonia Aquatic Life Support High
  • Source Unknown
  • High