Nishnabotna River IA 05-NSH-1412

Data Sources:

Class A1 - Indicator Bacteria: 2014-2016

Class A1 – pH:

Class BWW1 - Binomial Parameters:

Class BWW1 - Toxic Parameters:

Class BWW1 - Biological Sampling:

Benthic Macroinvertebrates:

Fish:

Overall:

Class BWW1- Continuous DO Monitoring: 2020

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 fish kill 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.

Fish and benthic macroinvertebrate biological sampling data from this segment can be found here: https://programs.iowadnr.gov/bionet/sites/388 and here: https://programs.iowadnr.gov/bionet/sites/928

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:

Class HH - Fish Tissue Sampling:

Class HH – Historic Assessment: 2012-2014

The results of USGS monitoring from 2012 and 2014 showed one of the 33 samples (3%) analyzed for DDE and three of the 33 samples (9%) analyzed for Dieldrin exceeded criteria. The sample collected on January 16, 2013 at USGS station 6810000 (near Hamburg) had a detectable level of DDE of 0.003 ug/l, thus exceeding the HH-fish criterion of 0.0022 ug/l. Levels of DDE for the remainder of the samples at this monitoring stations were reported as less than the levels of detection (0.002 ug/l and 0.005 ug/l). The samples collected on June 10, 2014, July 15, 2014, and September 16, 2014 at USGS station 06810000 (near Hamburg) had detectable levels of dieldrin of 0.004 ug/l, 0.003 ug/l, and 0.003 ug/l respectively, thus exceeding the HH-fish criterion of 0.00054 ug/l. Levels of dieldrin for the remainder of the samples at this monitoring stations were reported as less than the level of detection (0.008 ug/l). According to DNR’s assessment/listing methodology, if the average level of a toxic metal or pesticide is greater than its respective human health criterion, impairment ("WINOFI") of the Human Health use is indicated. The number of samples with detectable levels of DDE and dieldrin at these monitoring stations (1/33 and 3/33), however, is too few and the method detection level is far too high (~16 times greater than the HH criterion for dieldrin) to allow calculation of a meaningful summary statistic (e.g., mean) for DDE and dieldrin at this monitoring station. Based on sampling that shows detectable levels of DDE and dieldrin, however, the Class HH use was considered (evaluated) as “WINOFI.”