Iowa DNR

Water Quality Assessments

Impaired Waters List

Cedar River IA 02-CED-472

from W. Fk. Cedar R. (S4, T90N, R14W, Black Hawk Co.) to lowhead dam at Waverly in NW 1/4, S2, T91N, R14W, Bremer Co.

Assessment Cycle
Release Status
Result Period
2004 - 2006
HQR Class A1 Class B(WW-1) Class HH
Assessment Type
Integrated Report
Category 5a
Legacy ADBCode
IA 02-CED-0070_0
Overall Use Support
Aquatic Life Use Support
Fish Consumption
Not assessed
Primary Contact Recreation
Assessment Comments

Assessment is based on results of monthly monitoring from January 2004 through December 2006 at the IDNR ambient monthly monitoring station located near Janesville in Bremer Co. (STORET station 10090001).

Basis for Assessment

[Note:  Prior to the current (2008) Section 305(b) cycle, this river segment was designated only for Class B(WW) aquatic life uses, including fish consumption uses.   Due to changes in Iowa’s surface water classification that were approved by U.S.  EPA in February 2008 (see, and due to the completion of a Use Attainability Analysis, this segment is also now designated for Class A1 (primary contact recreation) uses.   This segment remains designated for warmwater aquatic life use (now termed Class B(WW1) uses), and for fish consumption uses (now termed Class HH (human health/fish consumption uses).]

SUMMARY:  The Class A1 (primary contact recreation) uses are assessed (monitored) as "partially supported" based on results of ambient monitoring for indicator bacteria during recreational seasons of 2004 through 2006.   The Class B(WW1) aquatic life uses are assessed (monitored) as "fully supported" based on results of ambient water quality monitoring from 2004 through 2006.   Fish consumption uses remain not assessed due to the lack of fish contaminant monitoring in this river segment.   The source of data for this assessment is the results of monthly monitoring from January 2004 through December 2006 at the IDNR ambient monthly monitoring station located near Janesville in Bremer Co.  (STORET station 10090001).    

EXPLANATION:  The Class A1 uses were assessed (monitored) as "partially supported” due to high levels of indicator bacteria.   Due to recent changes in Iowa’s Water Quality Standards, Iowa’s assessment methodology for indicator bacteria has changed.   Prior to 2003, the Iowa WQ Standards contained a high-flow exemption for the Class A1 criterion for indicator bacteria (fecal coliforms) designed to protect primary contact recreation uses:  the water quality criterion for fecal coliform bacteria (200 orgs/100 ml) did not apply "when the waters [were] materially affected by surface runoff."  Due to a change in the Standards in July 2003, E.  coli is now the indicator bacterium, and the high flow exemption was eliminated and replaced with language stating that the Class A criteria for E.  coli apply when Class A1, A2, or A3 uses “can reasonably be expected to occur.”  Because the IDNR Technical Advisory Committee on WQ Standards could not agree on what flow conditions would define periods when uses would not be reasonably expected to occur, all monitoring data generated for E.  coli during the assessment period, regardless of flow conditions during sample collection, will be considered for determining support of Class A1 uses for purposes of Section 305(b) assessments and Section 303(d) listings.  

The geometric mean level of indicator bacteria (E.  coli) in the 24 samples collected during recreational seasons of 2004 through 2006 (112 orgs/100ml) is below the Iowa Class A1 water quality criterion of 126 orgs/100ml.   However, seven of the 24 samples (29%) contained a level of E.  coli that exceeded Iowa’s single-sample maximum criterion of 235 orgs/100 ml.   According to U.S.  EPA guidelines for Section 305(b) reporting, if more than 10% of samples exceed this single-sample maximum criterion, the primary contact recreation uses should be assessed as "partially supported" (see pgs 3-33 to 3-35 of U.S.  EPA 1997b).   According to IDNR’s assessment/listing methodology, these results suggest that significantly greater than 10% of the samples exceed IDNR’s single-sample maximum criterion, thus suggesting that the Class A1 uses should be assessed as “partially supported/impaired”.  

The Class B(WW1) aquatic life uses are assessed (monitored) as "fully supported" based on results of monitoring from the IDNR ambient station near Janesville from 2004 through 2006.   Monitoring at this station showed no violations of Class B(WW1) water quality criteria for dissolved oxygen or ammonia-nitrogen in the 36 samples collected or for toxic metals in the 10 samples analyzed during this assessment period.   Levels of pesticides in the nine samples from this station were below Class B(WW1) criteria.   Levels of pH in this river segment, however, occasionally violate the Class B(WW1) criterion of 9.0 pH units.   One of the 36 samples (3%) had a pH value greater than the Class B(WW1) criterion of 9.0 units (9.2 pH units).   Because these violations are more related to natural conditions (i.e., high levels of primary productivity) than to a pollutant, the occurrence of high levels of pH in this river segment is not seen as a water quality impairment.   Also, according to U.S.  EPA guidelines (U.S.  EPA 1997b, page 3-17), a violation frequency of less than 10 % for conventional parameters such as dissolved oxygen and pH suggest "full support" of aquatic life uses.   Thus, the percentage of violations of the pH criterion at this station (3%) does not suggest an impairment of aquatic life uses in this stream segment.

Fish consumption uses are not assessed due to the lack of recent fish tissue monitoring in this river segment.

Monitoring and Methods
Assessment Key Dates
12/5/2006 Fixed Monitoring End Date
1/8/2004 Fixed Monitoring Start Date
230 Fixed station physical/chemical (conventional plus toxic pollutants)
420 Water column surveys (e.g. fecal coliform)
Monitoring Levels
Biological 0
Habitat 0
Physical Chemistry 3
Toxic 3
Pathogen Indicators 3
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
Pathogens Primary Contact Recreation Slight
  • Source Unknown
  • Slight