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
1998 - 2000
Assessment Type
Integrated Report
Category 0
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 and (2) USGS NAWQA monitoring of water quality and fish tissue near Conesville.

Basis for Assessment

SUMMARY:  The Class A (primary contact recreation) uses and the Class B(WW) aquatic life uses were assessed as "fully supported."  Fish consumption uses were not assessed.   The primary source of data for this assessment is monthly monitoring results from October 1999 through September 2001 at the IDNR ambient station located at the County Road G28 bridge NE of Conesville.   EXPLANATION: The Class A uses were assessed as "fully supported."  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."  Thirteen of the 15 samples collected from the Conseville station during the 2000 and 2001 recreational seasons were collected at flows not materially affected by surface runoff.   The geometric mean level of indicator bacteria (fecal coliforms) in these 13 non-runoff-affected samples (32 orgs/100ml) is well below the Iowa Class A water quality criterion of 200 orgs/100ml.   None of the 13 samples 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 in 2000 and 2001.   Monitoring at this station showed no violations of Class B(WW) water quality criteria for dissolved oxygen or ammonia-nitrogen in the 24 samples collected or for toxic metals and toxic organic compounds in the four samples analyzed during this biennial period.   Levels of pH, however, occasionally violated the Class B(WW) criterion of 9.0 pH units.   Four of the 24 samples had pH values greater than 9.0 units, with a maximum value of 9.2 units.   All violations occurred on days when dissolved oxygen levels were well above 100% saturation:  November 1, 1999 (pH=9.1; % DO saturation=130%), April 3, 2000 (pH=9.2; DO saturation=140%), August 7, 2001 (pH=9.1; DO saturation>>140%); September 5, 2001 (pH=9.1; DO saturation>140%).   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 occurrenc of high levels of pH in this river segment is not seen as a water quality impairment.   Fish consumption uses were not assessed.   The most recent fish tissue monitoring was conducted in 1995 as part of the USGS NAWQA project.   These data are now more than five years old and are considered too old for characterizing current water quality conditions.

Monitoring and Methods
Assessment Key Dates
9/5/2001 Fixed Monitoring End Date
10/14/1999 Fixed Monitoring Start Date
230 Fixed station physical/chemical (conventional plus toxic pollutants)
240 Non-fixed station physical/chemical (conventional + toxicants)
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