East Nishnabotna River IA 05-NSH-1415
from confluence with Fisher Cr. (S27 T69N R40W Fremont Co.) to Page/Montgomery county line
- Cycle
- 2026
- Current Phase
- Public Comment
- Overall IR
- 5 - Water is impaired or threatened and a TMDL is needed.
- Trend
- Stable
- Created
- 10/27/2025 3:09:48 PM
- Updated
- 1/14/2026 5:42:56 PM
The Class A1 use remains assessed as "not supported" based on historic levels of indicator bacteria (E. coli) that violated state water quality criteria. The Class BWW1 use was assessed as "not supported" based on a fish kill investigation and as "WINOFI" based on biological sampling data. The Class HH use was assessed as "fully supported" based on water quality monitoring data.
Data Sources: Data Source Data Source ID Data Type Data Age Site ID Site
Name Site
Description Iowa DNR 6 WQ CY 2014-2016, CY 2022-2024 10360001 East
Nishnabotna River near Shenandoah
Iowa DNR 6 BIO See Below 221 East
Nishnabotna River Shenandoah Iowa DNR 6 BIO See Below 1528 East
Nishnabotna River Rapp
Park and Recreation Area Site ID Data Source ID # Samples / # Years 2014 Geo. Mean 2015 Geo. Mean 2016 Geo. Mean Annual Geometric Mean Violation # Violations % Violations Significantly >10% Violations Assessment Type Support Level 10360001 6 24 / 3 991 772 561 Yes 17 71% Yes Evaluated Not Site ID Data Source ID # Samples / # Years Minimum Value Maximum Value Mean Value # Violations Violations needed for impairment Violates Significantly >10% Rule? Assessment Type Support Level 10360001 6 36 / 3 7.5 8.9 8.2 0 7 NO MONITORED FULL Site ID Data Source ID Parameter Name # Samples / # Years Minimum Value Maximum Value Mean Value # Violations # Acute / Chronic Violations Violations needed for impairment Violates Significantly >10% Rule? Assessment Type Support Level 10360001 6 Chloride 36 / 3 15 27 19 NA 0 / 0 7 NO MONITORED FULL 10360001 6 Dissolved Oxygen 36 / 3 7.5 14.2 11 0 NA / NA 7 NO MONITORED FULL 10360001 6 pH 36 / 3 7.5 8.9 8.2 0 NA / NA 7 NO MONITORED FULL 10360001 6 Sulfate 36 / 3 14 38 28 0 NA / NA 7 NO MONITORED FULL 10360001 6 Temperature 36 / 3 0 30.7 14.3 0 NA / NA 7 NO MONITORED FULL Site ID Data Source ID Parameter Name # Samples / # Years Maximum Value Mean Value Median Value # Acute / Chronic Violations >1 Acute / Chronic Violation Assessment Type Support Level 10360001 6 Ammonia 36 / 3 0.25 0.04 0.02 0 / 0 NO MONITORED FULL 10360001 6 Cadmium 17 / 2 0.5 0.5 0.5 0 / 0 NO MONITORED FULL 10360001 6 Chromium 17 / 2 8 1.71 0.5 0 / 0 NO MONITORED FULL 10360001 6 Copper 18 / 2 4.9 2.1 2 0 / 0 NO MONITORED FULL 10360001 6 Lead 17 / 2 1 1 1 0 / 0 NO MONITORED FULL 10360001 6 Nickel 17 / 2 2.9 1.8 1.8 0 / 0 NO MONITORED FULL 10360001 6 Selenium 36 / 3 4 1.6 2 0 / 0 NO MONITORED FULL 10360001 6 Silver 17 / 2 1 1 1 0 / 0 NO MONITORED FULL 10360001 6 Zinc 17 / 2 1.2 0.6 0.5 0 / 0 NO MONITORED FULL Benthic Macroinvertebrates: Site ID Date Drainage Area (mi2) Ecoregion Major Drainage BM Sample Gear BMIBI score BMIBI Class 47e BMIBI BIT BMIBI Pass/Fail 1528 9/24/24 1010 47e MO Floating Art Sub 31 Fair 54 Fail 221 8/6/24 1022 47e MO Floating Art Sub 48 Fair 54 Fail 221 8/12/20 1022 47e MO Floating Art Sub 24 Poor 54 Fail Site ID Date Drainage Area (mi2) Ecoregion Major Drainage Riffle Stream? FIBI score FIBI Class 47m FIBI BIT FIBI Pass/Fail 1528 9/24/24 1010 47e MO NA 44 Fair 31 Pass Community Assessment Type Assessment Result Support Level IR Category Reason Benthic
Macroinvertebrates Evaluated Fail (0/3) WINOFI Fish Evaluated Pass (1/1) Full Assessment was
evaluated because the drainage areas Overall Evaluated Fail WINOFI 3bu of the sample sites
were larger than the calibrated range. Class BWW1 – Fish kill Assessment: Following DNR IR fish kill methodology, the Class BWW1 aquatic life use
assessment based on the March 2024 fish kill should have resulted in a Category
3b potential impairment because a single fish kill occurred in this segment
during the IR data assessment period (2020-2024). However, given the magnitude
of the fish kill (~50 miles affected and ~750,000 fish killed), DNR IR staff
felt it was appropriate to place this segment in Category 4d. The fish kill was
caused by a “pollutant” or was suspected to be caused by a “pollutant”;
therefore, the Class BWW1 use was considered impaired. Since restitution for
the fish killed was received and/or the responsible party paid a fine, the
Class BWW1 use was placed in Category 4d (impaired but TMDL not required) and
not in Category 5b (impaired and TMDL required). DNR feels that (1) TMDLs
should not be required for a fish kill caused by a one-time illegal or
unauthorized release of a pollutant where enforcement action was taken and (2)
enforcement action is more appropriate and effective for addressing a
spill-related impairment than the TMDL process. In September of 2024, DNR Water Quality and Fisheries Bureaus conducted follow-up
biological sampling on this segment. The fish, benthic macroinvertebrate, and
freshwater mussel communities were sampled along with the collection of a grab
water quality sample and a physical habitat assessment was conducted. Results
from that sampling indicated that the biological communities had recovered to
pre-fish kill levels and were comparable to similarly sized sites in the
ecoregion. Details
about the 2024 fish kill can be found here: https://programs.iowadnr.gov/fishkill/events/1045 Details about the DNR
Contaminated Sites Section’s oversight can be found here: https://programs.iowadnr.gov/contaminatedsites/Site/Detail/2818 Details about the U.S.
Fish & Wildlife Service’s oversight can be found here: https://www.fws.gov/project/nishnabotna-fertilizer-spill
Class HH-F - Toxic Parameters: Site ID Data Source ID Parameter Name # Samples / # Years Maximum Value Mean Value Median Value Number of Non - Detects Mean Value > Criterion or MCL Assessment Type Support Level 10360001 6 Copper 18 / 2 4.9 2.1 2 2 NO MONITORED FULL Site ID Data Source ID Parameter Name # Samples per Year (2022/ 2023/2024) 2022 Mean 2023 Mean 2024 Mean # Non-Detects per Year (2022/ 2023/2024) Support Level per Year (2022/ 2023/2024) Assessment Type Support Level 10360001 6 Selenium 12/12/12 1.958 1.442 1.542 1/0/2 FS/FS/FS MONITORED FULL
Class A1 - Indicator Bacteria: 2014-2016
Class A1 – pH:
Class BWW1 - Binomial Parameters:
Class BWW1 - Toxic Parameters:
Class BWW1 - Biological Sampling:
Fish:
Overall:
Fish and benthic macroinvertebrate biological sampling data from this segment can be found here: https://programs.iowadnr.gov/bionet/sites/1528
and here: https://programs.iowadnr.gov/bionet/sites/221