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
2002 - 2004
Class B(WW)
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 2002-04 and IDNR/UHL biological sampling in 2000 and 2001.

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 lead and copper.   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 monthly (plus) ambient monitoring conducted during the 2002-2004 assessment period at the County Road C-70 bridge north of Sioux City (STORET station 10750001 (formerly station 950110)) and (2) DNR/UHL biological monitoring in 2000 and 2001.

EXPLANATION:  Monitoring at the IDNR monthly ambient monitoring station north of Sioux City showed no violations of Class B(WW) water quality criteria for dissolved oxygen or pH in the 46 samples analyzed or for pesticides in the 13 samples analyzed during the 2002-2004 assessment period.   Levels of ammonia-nitrogen and toxic metals, however, did violate the Class B(WW) criteria during the assessment period.   One of the 46 samples analyzed contained a level of ammonia nitrogen that exceeded state’s pH-dependent chronic water quality criteria for Class B(WW) waters  This violation occurred in the sample collected on July 11, 2002; this sample contained 1.9 mg/l of ammonia-nitrogen.   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, no more than one sample exceeds a criterion, aquatic life uses should be assessed as “fully supported” (see pg 3-18 of U.S.  EPA 1997b).   Compared to the previous (2004) assessment period, the conditions related to high levels of ammonia appear to have improved in this segment of the Floyd River.   During the 2000-2002 assessment period, three of the 50 samples analyzed violated Class B(WW) criteria for ammonia-nitrogen, thus indicating impairment of the Class B(WW) uses (see assessment developed for the 2004 assessment cycle for more information).  

While conditions relative to ammonia have improved since the 2004 assessment, violations due to toxic metals appear to have increased.   Two of the 15 samples analyzed for toxic metals contained levels of copper and lead that exceeded Class B(WW) criteria.   Violations of the chronic Class B(WW) copper criterion (35 ug/l) occurred on July 10, 2003 (40 ug/l) and on July 11, 2002 (110 ug/l (this level exceeds the acute criterion for copper of 60 ppb) and on July 10, 2003 (50 ug/l).   Also, two of 15 samples contained levels of lead that exceeded Class B(WW) chronic criterion of 30 ppb (violations occurred on July 10, 2003 (40 ug/l) and on July 11, 2002 (100 ug/l).   According to U.S.  EPA guidelines for Section 305(b) water quality assessments (U.S.  EPA 1997b, page 3-18), more than one violation of a water quality criterion for a toxic pollutant in an abundant data set (at least 10 samples over at three-year period) indicates impairment of aquatic life uses.   Thus, results of monitoring for both copper and lead suggest “non-support” of the Class B(WW) uses.

However, biological sampling results suggest the aquatic life uses should be assessed (evaluated) as partially supporting based on IDNR/UHL data collected in 2000 and 2001.   This evaluated biological assessment was based on data collected in 2000 and 2001 as part of the DNR/UHL stream monthly ambient sampling project.   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 2000 FIBI score was 45 (fair) and the BMIBI score was 28 (poor).   The 2001 BMIBI score was 56 (good).   The BMIBI average was 42.   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 from a statistical analysis of data collected at stream ecoregion reference sites from 1994-2004.   The FIBI BIC for this ecoregion is 31 and the BMIBI BIC for this ecoregion is 54.   This assessment is considered evaluated because the drainage area (882 mi2) above this 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 FIBI BIC and failed the BMIBI BIC, it is uncertain as to whether or not this segment is meeting the aquatic life criteria because it doesn’t fall in the calibrated watershed size.

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
12/7/2004 Fixed Monitoring End Date
1/8/2002 Fixed Monitoring Start Date
9/20/2001 Biological Monitoring
9/20/2000 Biological Monitoring
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 Fair
Causes and Sources of Impairment
Causes Use Support Cause Magnitude Sources Source Magnitude
Copper Aquatic Life Support Moderate
  • Source Unknown
  • Moderate
Lead Aquatic Life Support Moderate
  • Source Unknown
  • Moderate
Unionized Ammonia Aquatic Life Support Not Impairing
  • Source Unknown
  • Not Impairing