East Nishnabotna River IA 05-NSH-1816
from Page/Montgomery Co. line to state Highway 48 bridge approximately 1.5 miles north of Red Oak at east line of S8 T72N R38W Montgomery Co.
- Cycle
- 2026
- Current Phase
- Public Comment
- Overall IR
- 4 - Water is impaired or threatened and a TMDL has been completed or is not needed.
- Trend
- Stable
- Created
- 10/27/2025 3:10:16 PM
- Updated
- 1/15/2026 8:36:34 AM
The Class BWW1 use was assessed as "not supported" based on a fish kill investigation and "WINOFI" based on biological sampling data. The Class HH (fish consumption) use was assessed as "fully supported" based on fish tissue sampling data. All other designated uses were "not assessed."
Data Sources: Data Source Data Source ID Data Type Data Age Site ID Site Name Site Description Iowa DNR 6 BIO See Below 680 East Nishnabotna
River Red Oak – DS1 Iowa DNR 6 FT See Below 1382 East Nishnabotna
River (U) Red Oak Boat Ramp Benthic
Macroinvertebrates: Site ID Date Drainage Area (mi2) Ecoregion Major Drainage BM Sample Gear BMIBI score BMIBI Class 47e BMIBI BIT BMIBI Pass/Fail 680 9/25/24 895 47e MO Floating Art Sub 37 Fair 54 Fail Site ID Date Drainage Area (mi2) Ecoregion Major Drainage Riffle Stream? FIBI score FIBI Class 47m FIBI BIT FIBI Pass/Fail 680 9/25/24 895 47e MO NA 42 Fair 31 Pass Community Assessment Type Assessment Result Support Level IR Category Reason Benthic
Macroinvertebrates Evaluated Fail (0/1) WINOFI Fish Evaluated Pass (1/1) Full Assessment was
evaluated because the drainage area Overall Evaluated Fail WINOFI 3bu of the sample site
was 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 - Fish Tissue Sampling: Site ID Biopart Year Species # in sample / # of samples Avg Length (cm) (Avg) Hg (ppm) Chlordane (ppm) Sum PCBs (ppm) 1382 tissue plug 2021 common carp 10 55.4 0.088 1382 tissue plug 2020 channel catfish 10 49.4 0.093 Support Level Full
Class A1 - No Data
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/680