Iowa DNR

Water Quality Assessments

Impaired Waters List

Iowa River IA 02-IOW-622

from south corporate limit of Wapello (S35, T74N, R3W, Louisa Co.) to Long Cr (S1, T74N, R4W, Louisa Co.)

Assessment Cycle
Release Status
Result Period
2000 - 2002
Assessment Type
Integrated Report
Category 2b
Legacy ADBCode
IA 02-IOW-0010_2
Overall Use Support
Aquatic Life Use Support
Fish Consumption
Primary Contact Recreation
Not assessed
Assessment Comments

Assessment is based (evaluated) on results of (1) 1999-2002 biocriteria (benthic macroinvertebrate) data, (2) USGS/NAWQA monitoring at Wapello from 2000-02, and (3) U.S. EPA/IDNR fish tissue (RAFT) monitoring near Wapello in 1999 and 2001.

Basis for Assessment

SUMMARY:  The Class A (primary contact recreation) uses are not assessed due to the lack of information upon which to base an assessment.   The Class B(WW) aquatic life uses are assessed (monitored) as "partially supported" based on results of biological (benthic macroinvertebrate) monitoring conducted from 1999 through 2002.   Fish consumption uses remain assessed (monitored) as "fully supported" based on results of fish contaminant monitoring in 1999 and 2001.   Sources of data for this assessment include (1) results of ambient water quality monitoring at Wapello conducted from February 2000 through August 2002 as part of the USGS NAWQA program, (2) results of biological monitoring conducted from 1999 through 2002 as part of the IDNR/UHL ambient water quality monitoring program and the IDNR/UHL stream biocriteria project, and (3) results of U.S.EPA/IDNR fish contaminant (RAFT) monitoring at Wapello in 1999 and 2001.  

EXPLANATION:  The monitoring conducted on the Iowa River at Wapello from October 1998 through August 2002 by USGS (station 05465500) has not included analysis for fecal coliform bacteria (in summer 1997, USGS switched from fecal coliform bacteria to E.  coli as the bacterial indicator for NAWQA monitoring; until July 2003, the Iowa Water Quality Standards specified fecal coliform bacteria as water quality criterion to protect Class A (primary contact recreation) uses).   Thus, due to lack of information on indicator bacteria, an assessment of support of the Class A uses was not developed.  

Regarding support of the Class B(WW) uses, results of the USGS/NAWQA monitoring from February 2000 through August 2002 showed (1) no violations of Class B(WW) water quality criteria for pH, dissolved oxygen, or ammonia-nitrogen in the approximately 30 samples collected and (2) no violations of the Class B(WW) chronic water quality criteria for chlorpyrifos, DDE, or dieldrin in the approximately 30 samples analyzed.   Note:  the assessment of aquatic life uses developed for the 2000 report ("partially supported”) was based on two violations of the Class B(WW) chronic WQ criterion for dieldrin in the 52 samples collected between March 1996 and August 1998.   Because no dieldrin was detected in the 34 samples collected between October 1998 and September 2001, this assessment was changed to "fully supported" for the 2002 report.   USGS monitoring conducted from September 2001 through August 2002 showed no levels of dieldrin above the level of detection (0.005 ug/l) thus confirming the lack of violations of dieldrin criteria in this river reach.

Despite the results of ambient chemical/physical monitoring that suggest “full support” of aquatic life uses, results of biological monitoring suggest only “partial support” of these uses.   Biological data were collected in 1999, 2000, 2001, and 2002 as part of the IDNR/UHL ambient water quality monitoring program and the DNR/UHL stream biocriteria project.   A series of biological metrics which reflect stream water quality and habitat integrity were calculated from the biocriteria sampling data.   The biological metrics used for this assessment are based on the numbers and types of benthic macroinvertebrate taxa that were collected in the river sampling reach.   The biological metrics were combined to make a benthic macroinvertebrate index (BM-IBI).   The index ranks the biological integrity of a stream sampling reach on a rising scale from 0 (minimum) to 100 (maximum).   The 1999, 2000, 2001, and 2002 BM-IBI scores were 36 (fair), 36 (fair), 27 (poor), and 39 (fair) respectively.   Thus, the aquatic life use support was assessed as “partially supporting” (=PS), based on a comparison BM-IBI scores with biological assessment criteria established specifically for the 2002 Section 305(b) report.   The biological assessment criteria were determined from a statistical analysis of data collected at stream ecoregion reference sites from 1994-2001.   The causes and sources of this potential impairment are not known but may include problems with habitat quality and/or occasionally poor chemical water quality.   The assessment type is considered  “evaluated” (of lower confidence) because the size of the segment’s watershed exceeds the range of reference condition watershed sizes used to calibrate the benthic macroinvertebrate and fish bioassessment indexes.   For this assessment, the drainage area for the segment (approximately 12,500 mi2) far exceeds the maximum drainage area cutoff (500 mi2) that IDNR has established for use of BMIBI and FIBI data.   Therefore, IDNR considers the aquatic life use impairments indicated by these data as “evaluated” assessments that are not appropriate for Section 303(d) listing (Category 5 of the Integrated Report).   IDNR does, however, consider these impairments as appropriate for listing under either Category 2b or 3b of the Integrated Report (waters potentially impaired and in need of further investigation).

Fish consumption uses remained assessed as "fully supported" based on results of EPA/DNR fish tissue (RAFT) monitoring near Wapello in 1999 and 2001 that showed levels of contaminants in the composite sample of whole-fish common carp remain below ½ of the respective FDA action levels and DNR levels of concern (see assessments for the 2000 and 2002 reports for more information).   This site was again monitored as part of the 2003 RAFT program; the results from this monitoring, however, are not yet available.

Monitoring and Methods
Assessment Key Dates
9/24/2002 Biological Monitoring
8/6/2002 Fixed Monitoring End Date
9/14/2001 Biological Monitoring
9/5/2001 Fish Tissue Monitoring
10/17/2000 Biological Monitoring
2/1/2000 Fixed Monitoring Start Date
10/15/1999 Biological Monitoring
8/20/1999 Fish Tissue Monitoring
315 Regional reference site approach
320 Benthic macroinvertebrate surveys
260 Fish tissue analysis
230 Fixed station physical/chemical (conventional plus toxic pollutants)
Monitoring Levels
Biological 3
Habitat 0
Physical Chemistry 3
Toxic 0
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
Cause Unknown Aquatic Life Support Moderate
  • Source Unknown
  • Moderate