Iowa DNR

Water Quality Assessments

Impaired Waters List

East Nodaway River IA 05-NOD-1391

mouth (S6 T67N R36W Page Co.) to confluence with Long Branch Cr at S17-18 line T70N R35W Taylor Co.

Assessment Cycle
Release Status
Data Collection Period
Overall IR Category
5 - Water is impaired or threatened and a TMDL is needed.
9/27/2016 8:12:46 AM
9/27/2016 11:38:17 AM
Assessment conducted in accordance with Iowa's 2016 IR methodology
Use Support
Class A1
Partially Supported
Bacteria: Indicator Bacteria- E. coli
Support Level
Partially Supported
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 BWW1
Biological: low fish & invert IBIs- cause unknown
Support Level
Water in Need of Further Investigation (WINOFI)
Impairment Code
3b-c - Use potentially biologically impaired based on calibrated IBI metrics.
Cause Magnitude
Unknown: Source Unknown
Source Confidence
Cycle Added
Impairment Rationale
Low Biotic Index
Data Source
Biological monitoring: Iowa DNR WQMA
Class HH
Not Assessed
General Use
Not Assessed
Impairment Delistings
No delistings for this assessment cycle.
Assessment Summary

The presumptive Class A1 (primary contact recreation) uses are assessed (monitored) as "not supported" (IR 5p) due to levels of indicator bacteria that violate state water quality criteria. The Class B(WW1) aquatic life uses are assessed (evaluated) as "partially supported" (IR 3b-c) based on results of biological sampling in 2004 and 2012. Fish consumption uses remain assessed "not assessed" (IR 3a) due to the lack of fish contaminant monitoring in this river reach. This assessment is based on (1) results of IDNR/SHL monthly ambient water quality monitoring conducted during the 2012-2014 assessment period at the State Highway 2 bridge 2 miles east of Clarinda (STORET station 10730002 (formerly station 780809)) and (2) results of IDNR/SHL biocriteria sampling in 2004 and 2012.

Assessment Explanation

[Note: Prior to the 2008 Section 305(b) cycle, this stream 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, this segment is also now presumptively 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).]

The presumptive Class A1 (primary contact recreation) uses are assessed (monitored) as "partially supported" based on levels of indicator bacteria that exceeded state water quality criteria.  The geometric means of indicator bacteria (E. coli) in the 24 samples collected during the recreational seasons of 2012 through 2014 at the East Nodaway River near Clarinda were as follows: the 2012 geometric mean was 812 orgs/100 ml, the 2013 geometric mean was 264 orgs/100 ml, and the 2014 geometric mean was 467 orgs/100 ml.  All three recreation season geometric means exceeded the Class A1 geometric mean criterion of 126 orgs/100 ml.  Fifteen of the combined 24 samples (62%) exceeded Iowa’s 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 the geometric mean is greater than 126 orgs/100 ml., the primary 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 uses, these uses are assessed as "partially supported."

Results of chemical/physical water quality monitoring at the East Nodaway River near Clarinda suggest “full support” of the aquatic life uses. Monitoring showed no violations of Class B(WW1) water quality criteria for 36 Ammonia samples (maximum = 0.8 mg/L), 36 Dissolved Oxygen samples (minimum = 5.8 mg/L), 36 pH samples (range = 7.3 to 8.8), 36 Temperature samples (maximum = 27.7° c), 36 Chloride samples (maximum = 27 mg/L), or 36 Sulfate samples (maximum = 96 mg/L) occurred during monitoring from January 2012 to December 2014. According to U.S.  EPA guidelines for Section 305(b) water quality assessments (U.S.  EPA 1997b, page 3-17), the EPA guidelines allow up to 10% violations of these conventional parameters before impairment of water quality is indicated. Thus, these results thus suggest “full support” of the Class B(WW1) aquatic life uses.

Results of biological sampling, however, suggest that the Class B(WW1) uses should be assessed (evaluated) as "partially supported" based on IDNR/SHL biocriteria sampling in 2004 and 2012. The 2004 FIBI score was 23 (poor) and the BMIBI score was 46 (fair). The 2012 FIBI score was 39 (fair) and the BMIBI score was 46 (fair). This suggests the aquatic life use support be assessed as partially supported (=PS), 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 FIBI BIC for this ecoregion is 31 and the BMIBI BIC for this ecoregion is 54. This segment passed the FIBI BIC 1/2 times and passed the BMIBI BIC 0/2 times in the last nine years.

This aquatic life assessment is now considered "evaluated" 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 in a recent five year period to be considered “monitored”. This segment had multiple samples collected in the previous nine years; however, the multiple samples were not collected during a recent five year period. According to IDNR’s assessment/listing methodology, impairments based on “evaluated” assessments are of lesser confidence and are thus 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 remain "not assessed" due to the lack of recent fish tissue monitoring in this river reach.


Monitoring and Methods
Assessment Key Dates
1/4/2012 Fixed Monitoring Start Date
12/1/2014 Fixed Monitoring End Date
8/21/2012 Biological Monitoring
10/13/2004 Biological Monitoring
150 Monitoring data more than 5 years old
230 Fixed station physical/chemical (conventional plus toxic pollutants)
315 Regional reference site approach
320 Benthic macroinvertebrate surveys
330 Fish surveys
380 Quantitative physical habitat assessment
420 Indicator bacteria monitoring