Iowa DNR

Water Quality Assessments

Impaired Waters List

Cedar River IA 02-CED-449

mouth (S20, T75N, R4W, Louisa Co.) to confluence with Sugar Cr. in S17, T78N, R2W, Muscatine Co.

Assessment Cycle
Release Status
Result Period
2000 - 2002
Assessment Type
Integrated Report
Category 1
Legacy ADBCode
IA 02-CED-0010_0
Overall Use Support
Aquatic Life Use Support
Fish Consumption
Not assessed
Primary Contact Recreation
Assessment Comments

Assessment is based on results of (1) DNR monthly ambient station NE of Conesville from 2000-02 and (2) USGS NAWQA monitoring of fish tissue near Conesville in 1995.

Basis for Assessment

SUMMARY:  The Class A (primary contact recreation) uses and the Class B(WW) aquatic life uses were assessed (monitored) as "fully supported."  Fish consumption uses are assessed (evaluated) as “fully supported” based on results of fish contaminant monitoring in 1995.   The sources of data for this assessment are (1) results of monthly monitoring from 2000 through 2002 at the IDNR ambient station located at the County Road G28 bridge NE of Conesville (IDNR station 10700001), and (2) results of fish contaminant monitoring conducted as part of the USGS NAWQA program in 1995.  

EXPLANATION: The Class A uses were assessed as "fully supported" based on results of IDNR ambient monitoring near Conesville.   For purposes of Section 305(b) assessments, DNR uses the long-term average monthly flow plus one standard deviation of this average to identify river flows that are materially affected by surface runoff.   According to the Iowa Water Quality Standards (IAC 1990:8), the water quality criterion for fecal coliform bacteria (200 orgs/100 ml) does not apply "when the waters are materially affected by surface runoff."  Eighteen of the 21 samples collected from the Conesville station during the 2000, 2001, and 2002 recreational seasons were collected at flows not materially affected by surface runoff.   The geometric mean level of indicator bacteria (fecal coliforms) in these 18 non-runoff-affected samples (47 orgs/100ml) is well below the Iowa Class A water quality criterion of 200 orgs/100ml.   One of the 18 samples (6%) exceeded the U.S.  EPA-recommended single-sample maximum value of 400 orgs/100 ml (see pgs 3-33 to 3-35of U.S.  EPA 1997b).   According to U.S.  EPA guidelines, these data suggest that the Class A uses should be assessed as "fully supported."  

The Class B(WW) aquatic life uses were assessed as "fully supported" based on results of monitoring from the IDNR ambient station near Conesville from 2000 through 2002.   Monitoring at this station showed no violations of Class B(WW) water quality criteria for dissolved oxygen or ammonia-nitrogen in the 36 samples collected or for pesticides in the nine samples analyzed during this assessment period.   Levels of pH, however, occasionally violated the Class B(WW) criterion of 9.0 pH units.   Five of the 36 samples had pH values greater than 9.0 units, with a maximum value of 9.2 units.   Violations tended to occur on days when dissolved oxygen levels were well above 100% saturation (see assessment for the 2002 report).These conditions suggest that high levels of primary productivity resulted in the high levels of pH.   Because these violations are more related to natural conditions than to pollution, the occurrence of high levels of pH in this river segment is not seen as a water quality impairment.   Fish consumption uses are assessed (evaluated) as “fully supported” based on results of fish contaminant monitoring conducted by USGS in 1995 as part of the NAWQA project.   However, because these data are now considered too old (greater than five years) to accurately characterize current water quality conditions, the assessment category is changed from "monitored" (indicating an assessment with relatively high confidence) to "evaluated" (indicating an assessment with relatively lower confidence).

Monitoring and Methods
Assessment Key Dates
12/2/2002 Fixed Monitoring End Date
1/3/2000 Fixed Monitoring Start Date
9/30/1995 Fish Tissue Monitoring
230 Fixed station physical/chemical (conventional plus toxic pollutants)
260 Fish tissue analysis
420 Water column surveys (e.g. fecal coliform)
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