Iowa DNR
Iowa DNR

ADBNet

Water Quality Assessments
Impaired Waters List

West Nishnabotna River IA 05-NSH-1446

from confluence with Elk Cr. (S36 T81N R38W Shelby Co.) to the Crawford-Carroll county line (west line S36 T82N R37W Crawford Co.)

This is a DRAFT assessment
Draft assessments may change without notice
Overall IR
5 - Water is impaired or threatened and a TMDL is needed.
Trend
Stable
Current Phase
Public Comment
Created
10/27/2025 3:08:53 PM by
Updated
12/1/2025 10:09:48 AM by
Use Support
Class A1
Recreation - Primary contact
Not Assessed
Class BWW2
Aquatic Life - Warm Water Type 2
Not Supported
Support Level
Not Supported
Impairment Code
5b-v - Biological - verified
Cause Magnitude
Slight
303(d) Listing Status
Continuing
Source
Unknown: Source Unknown
Source Confidence
Low
Cycle Added
2006
Impairment Rationale
Low Biotic Index
Data Source
Biological monitoring: Iowa DNR WQMA
TMDL Priority
Tier IV
No delistings for this assessment cycle.
Documentation
Assessment Summary

The Class BWW2 use was assessed as “not supported” based on biological sampling data. All other designated uses were "not assessed."

Assessment Explanation

Data Sources:

Data Source

Data Source ID

Data Type

Data Age

Site ID

Site Name

Site Description

Iowa DNR

6

BIO

See Below

6

West Nishnabotna River

Shelby County Upper Nishnabotna Habitat Area

Iowa DNR

6

WQ

See Below

367

West Nishnabotna River

Irwin – REMAP #60


Presumptive Class A1 – No Data


Class BWW2 - Biological Sampling:


Benthic Macroinvertebrates:

Site ID

Date

Drainage Area (mi2)

Ecoregion

Major Drainage

BM Sample Gear

BMIBI score

BMIBI Class

47e BMIBI BIT

BMIBI Pass/Fail

6

8/14/23

86.1

47e

MO

Surber

46

Fair

54

Fail

6

8/19/20

86.1

47e

MO

Surber

52

Fair

54

Fail


Fish:

Site ID

Date

Drainage Area (mi2)

Ecoregion

Major Drainage

Riffle Stream?

FIBI score

FIBI Class

47e FIBI BIT

FIBI Pass/Fail

6

8/14/23

86.1

47e

MO

NA

37

Fair

31

Pass

6

8/19/20

86.1

47e

MO

NA

42

Fair

31

Pass


Overall:

Community

Assessment Type

Assessment Result

Support Level

IR Category

Reason

Benthic Macroinvertebrates

Monitored

Fail (0/2)

Not

Fish

Monitored

Pass (2/2)

Full

Assessment was monitored because the assessment was

Overall

Monitored

Fail

Not

5bv

based on samples collected in a recent five-year period.


Class BWW2- Continuous DO Monitoring:

Site ID

Data Source ID

# Days Monitoring (2019)

DO Criteria Type

# 2019 violations / Violations needed for impairment

Violates Annual Significantly >10% Rule?

Assessment Type

Support Level

24 hr

0/4

No

367

6

14

16 hr

0/4

No

Evaluated

Full

Monitoring and Methods
Assessment Key Dates
8/14/2023
Biological Monitoring
8/19/2020
Biological Monitoring
8/26/2019
Monitoring Start
9/9/2019
Monitoring End
Methods
200
Physical/Chemical Monitoring
315
Regional reference site approach
320
Benthic macroinvertebrate surveys
330
Fish surveys