Iowa DNR

Water Quality Assessments

Impaired Waters List

Nishnabotna River IA 05-NSH-1412

IA/MO line to (S26 T67NR42W Fremont Co.) to confluence of E. Nishnabotna and W. Nishnabotna rivers in S2 T67N R42W Fremont Co.

Assessment Cycle
Result Period
2002 - 2004
Class B(WW)
Assessment Methodology
Assessment Type
Integrated Report
Category 2b
Legacy ADBCode
IA 05-NSH-0010_0
Overall Use Support
Aquatic Life Use Support
Fish Consumption
Assessment Comments

Assessment is based on results of (1) IDNR/UHL biological (REMAP) monitoring in 2003, (2) USGS ambient water quality monitoring in 2004, and (3) EPA/IDNR fish contaminant (RAFT) monitoring in 2002.

Basis for Assessment

SUMMARY:  The Class B(WW) aquatic life uses are assessed (evaluated) as “partially supported” based on results of biological monitoring in 2003.   The fish consumption uses are assessed (monitored) as fully supported based on results of fish contaminant monitoring in 2002.   The sources of data for this assessment include the results of (1) USGS ambient water quality monitoring conducted on the Nishnabotna River at Hamburg from March to September 2004, (2) IDNR/UHL biological (REMAP) monitoring in 2003, and (3) EPA/IDNR fish contaminant (RAFT) monitoring in 2002.  

EXPLANATION:  The Class B(WW) aquatic life uses are assessed (evaluated) as "partially supported" based on results of IDNR/UHL biological (REMAP) monitoring in 2003.   A series of biological metrics that reflect stream water quality and habitat integrity were calculated from the biocriteria 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 2003 FIBI score was 5 (poor) and the BMIBI score was 55 (fair).  The aquatic life use support was assessed (evaluated) as Partially Supporting (= PS), based on a comparison of the FIBI and BMIBI scores with biological impairment criteria (BIC) established from a statistical analysis of data collected at stream ecoregion reference sites from 1994-2004.   The FIBI BIC for this ecoregion is 31 and the BMIBI BIC for this ecoregion is 54.   This assessment is considered evaluated because the drainage area (2,812 mi2) above this sampling site was greater than the maximum limit (500 mi2) that was used to calibrate the Iowa wadeable stream impairment criteria.   Even though this site failed the FIBI BIC and passed the BMIBI BIC, it is uncertain as to whether or not this segment is meeting the aquatic life criteria because it doesn’t fall in the calibrated watershed size.   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).

In contrast to the results of biological monitoring that suggest only “partial support” of the Class B(WW) uses, results of water quality monitoring by the U.S.  Geological Survey above Hamburg in 2004 suggest “full support” of these uses.   No violations of state water quality criteria occurred in the nine samples analyzed for dissolved oxygen, pH, ammonia, chlorpyrifos, DDE, and dieldrin.   Although these results indicate “full support” of the aquatic life uses of this river segment, the number of samples is relatively low and does not meet IDNR guidelines for developing a “monitored” (i.e., higher confidence) assessment.   Thus, the assessment type is considered “evaluated” (lower confidence).  

Fish consumption uses were assessed (monitored) as “fully supported” based on results of U.S.EPA/IDNR fish contaminant (RAFT) monitoring near Hamburg in 2002.   The composite samples of fillets from common carp had low levels of contaminants.   Levels of primary contaminants in the composite sample of common carp fillets were as follows: mercury: 0.085 ppm; total PCBs: 0.093 ppm; and technical chlordane: 0.03 ppm.   [Note:  Typically, samples of both bottom-feeding fish (e.g., common carp) and predator species (e.g., largemouth bass) are collected at RAFT status sites such as the Nishnabotna River at Hamburg.   Predator species, however, are naturally rare in rivers of southwestern Iowa, and RAFT status samples from these rivers typically contain only the bottom-feeder sample.]  The existence of, or potential for, a fish consumption advisory is the basis for Section 305(b) assessments of the degree to which Iowa’s lakes and rivers support their fish consumption uses.   Prior to 2006, IDNR used action levels published by the U.S Food and Drug Administration to determine whether consumption advisories should be issued for fish caught as part of recreational fishing in Iowa.   In an effort to make Iowa’s consumption more compatible with the various protocols used by adjacent states, the Iowa Department of Public Health, in cooperation with Iowa DNR, developed a risk-based advisory protocol.   This protocol went into effect in January 2006 (see for more information on Iowa’s revised fish consumption advisory protocol).   Because the revised (2006) protocol is more restrictive than the previous protocol based on FDA action levels; fish contaminant data that previously suggested “full support” may now suggest either a threat to, or impairment of, fish consumption uses.   This scenario, however, does not apply to the fish contaminant data generated from the 2002 RAFT sampling conducted in this assessment segment:  the levels of contaminants do not exceed any of the new (2006) advisory trigger levels, thus indicating no justification for issuance of a consumption advisory for this waterbody.

Monitoring and Methods
Assessment Key Dates
8/12/2003 Biological Monitoring
9/9/2002 Fish Tissue Monitoring
260 Fish tissue analysis
240 Non-fixed station physical/chemical (conventional + toxicants)
220 Non-fixed station physical/chemical monitoring (conventional pollutant only)
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
Monitoring Levels
Biological 4
Habitat 4
Physical Chemistry 3
Toxic 3
Pathogen Indicators 0
Other Health Indicators 0
Other Aquatic Life Indicators 0
# of Bio Sites 1
BioIntegrity Fair
Causes and Sources of Impairment
Causes Use Support Cause Magnitude Sources Source Magnitude
Cause Unknown Aquatic Life Support Slight
  • Source Unknown
  • Slight