Iowa DNR

Water Quality Assessments

Impaired Waters List

Beaver Creek IA 02-CED-555

mouth (S34 T90N R14W Black Hawk Co.) to confluence with South Beaver Cr. in S25 T90R R17W Butler Co.

Assessment Cycle
Release Status
Release Period
2012 - 2014
8/17/2016 10:55:17 AM
Overall IR Category
5 - Water is impaired or threatened and a TMDL is needed.
Last Updated
12/1/2016 3:20:36 PM
Use Support
Class A2
Secondary contact
Fully Supporting
Class A3
Children's contact
Partially Supporting
Bacteria: Indicator Bacteria- E. coli
Impairment Code
5p - Impairment occurs on a waterbody with a presumptive A1 or B(WW1) use.
Cause Magnitude
Unknown: Source Unknown
Source Confidence
Cycle Added
Impairment Rationale
Geometric mean criterion exceeded
Data Source
Ambient monitoring: Iowa DNR-rivers
TMDL Priority
Tier III
Class B(WW-1)
Aquatic Life
Warm Water Type 1
Fully Supporting
Class HH
Human Health
Not Assessed
General Use
General Use water
Not Assessed
Impairment Delistings
No delistings for this assessment cycle.
Assessment Summary

The Class A1/A3 (primary contact recreation) uses are assessed (monitored) as "partially supported" (IR 5a) due to levels of indicator bacteria that violate state water quality criteria.  The Class A2 (secondary contact recreation uses) are assessed as “fully supporting” (IR 2a).  The Class B(WW1) aquatic life uses are assessed (monitored) as “fully supported” (IR 2a) based on results of IDNR ambient water quality monitoring, IDNR/SHL biological data and IDNR Fisheries data.  Fish consumption uses remain "not assessed" (IR 3a) due to the lack of fish contaminant monitoring in this stream segment.  The sources of data for this assessment are (1) the results of IDNR monthly ambient monitoring from January 2012 through December 2014 at the county road T75 bridge approximately 3.5 miles northwest of Cedar Falls (STORET station 10070001), (2) the results of IDNR/SHL biological sampling in 2003, 2012, 2013 and 2014 and (3) 2001 IDNR Fisheries sampling. 

Assessment Explanation

The Class A1/A3uses are assessed as "partially supported" based on results of ambient monitoring for indicator bacteria (E. coli).  The geometric means of indicator bacteria (E. coli) in the 24 samples collected during the recreational seasons of 2012 through 2014 at IDNR ambient station 10070001 were as follows:  the 2012 geometric mean was 297 orgs/100 ml, the 2013 geometric mean was 226 orgs/100 ml, and the 2014 geometric mean was 114 orgs/100 ml.  The 2012 and 2013 geometric means very slightly exceed the Class A1/A3 criterion of 126 orgs/100 ml; the 2014 geometric mean is below this criterion.  Eleven of the 24 samples (46%) exceeded the Class A1 single-sample maximum criterion of 235 orgs/100 ml.  According to U.S. EPA guidelines for Section 305(b) reporting and IDNR’s assessment/listing methodology, if a recreation season geometric mean exceeds the respective water quality criterion, the contact recreation uses should be assessed as “impaired” (see pgs 3-33 to 3-35 of U.S. EPA 1997b).  Thus, because at least one recreation season geometric mean exceeded criteria for Class A1/A3 uses, these uses are assessed as “impaired.”  Similar to the previous (2010-2012) monitoring period, the results of bacteria monitoring from 2012 through 2014 at IDNR ambient station 10070001 show that all recreation season geometric means meet the Class A2 geometric mean criterion of 630 orgs/100 ml, and only one of the 24 samples (4%) exceeds Iowa’s single-sample maximum criterion.  These results suggest that the Class A2 secondary contact recreation uses should be assessed as “fully supporting”. 

The Class B(WW1) aquatic life uses remain assessed as “fully supported” based on results of both chemical/physical and biological monitoring.  Results of IDNR ambient water quality monitoring station NW of Cedar Falls during the 2012-2014 assessment period showed no violations of Class B(WW) water quality criteria for dissolved oxygen, pH, ammonia-nitrogen, temperature, chloride, or sulfate in the 36 samples collected. 

The assessment of the Class B(WW1) aquatic life uses as “fully supporting” remains partially based on results of biological monitoring conducted in 2003, 2012, 2013 and 2014 by IDNR/SHL as part of the REMAP and large river sampling projects and on data collected in 2001 by the IDNR Fisheries bureau.  A series of biological metrics which reflect stream water quality and habitat integrity were calculated from the biological 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 2001 IDNR Fisheries FIBI score was 62 (good).  The 2003 FIBI score was 45 (fair) and the 2003 BMIBI score was 77 (excellent).  The 2012 BMIBI score was 76 (excellent), the 2013 BMIBI score was 57 (good) and the 2014 BMIBI score was 56 (good).  The aquatic life use support was assessed as fully supporting (=FS), based on a comparison of the FIBI and BMIBI scores with biological impairment criteria (BIC) established for previous Section 305(b) reports.  The biological impairment criteria were determined from a statistical analysis of data collected at stream ecoregion reference sites from 1994-2008.  The non-riffle FIBI BIC for this ecoregion is 44 and the artificial substrate BMIBI BIC for this ecoregion is 52.  This segment passed the FIBI BIC 2/2 times in the last 14 years and passed the BMIBI BIC 4/4 times in the last 12 years. 

This aquatic life assessment is now considered "monitored" based on a change in the 2010 IDNR assessment methodology.  IDNR now requires a segment have two or more biological samples collected from the segment in multiple years over a five-year period to be considered “monitored”.  This segment had three BMIBI samples collected between 2012 and 2014. 

Fish consumption uses remain "not assessed" due to the lack of fish contaminant monitoring in this stream reach.

Monitoring and Methods
Assessment Key Dates
8/14/2003 Biological Monitoring
8/6/2012 Biological Monitoring
10/9/2013 Biological Monitoring
1/5/2012 Fixed Monitoring Start Date
12/3/2014 Fixed Monitoring End Date
10/9/2014 Biological Monitoring
8/14/2001 Biological Monitoring
220 Non-fixed station physical/chemical monitoring (conventional pollutant only)
230 Fixed station physical/chemical (conventional plus toxic pollutants)
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
420 Water column surveys (e.g. fecal coliform)
150 Monitoring data more than 5 years old