Upper Iowa River IA 01-UIA-239
from confluence with Trout Cr. (S9 T98N R7W Winneshiek Co.) to confluence with Tenmile Cr. in S1 T98N R9W Winneshiek Co.
- 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 3:08:48 PM
- Updated
- 12/23/2025 8:55:24 AM
The Class A1 use remains assessed as “not supported” due to levels of indicator bacteria (E. coli) that exceeded state water quality criteria. The Class BWW1 use remains assessed as "not supported" based on results of a 1998-99 statewide assessment of freshwater mussels in Iowa streams and on the results of a 2012 mussel survey. The Class HH use is still assessed as “not supported” based on the existence of a historical fish consumption advisory for this segment of the Upper Iowa River.
Data Sources: Data Source Data Source ID Data Type Data Age Site ID Site Name Site Description NEIARCD 19 WQ CY 2012-2014 191910010 Upper Iowa River
Freeport Site 17 Iowa DNR 6 BIO See Below 1411 Upper Iowa River City of Decorah Iowa DNR 6 FT See Below 1094 Upper Iowa River NE of Freeport Site ID Data Source ID # Samples / # Years 2012 Geometric Mean 2013 Geometric Mean 2014 Geometric Mean Annual Geometric
Mean Violation # Violations % Violations Significantly
>10% Violations Assessment Type Support Level 191910010 19 20 / 3 60 463 616 Yes 9 45% Yes Evaluated Not Fish: BioNet Site ID Date Drainage Area (mi2) Ecoregion Major Drainage/Thermal Riffle Stream? FIBI score FIBI Class 52b FIBI BIT FIBI Pass/Fail 1411 8/12/24 516 52b MS/WW NA 76 Excellent 52 Pass Community Assessment Type Assessment Result Support Level IR Category Reason Fish Evaluated Pass (1/1) Full Assessment was evaluated because the drainage area of the site Overall Evaluated Pass Full 1 used for the assessment was greater than the calibrated range. Freshwater Mussel Survey # Freshwater Mussel
Species # Freshwater Mussel
Species Increase/Decrease % Freshwater Mussel
Species Increase/Decrease Assessment Type Support Level IR Category 1984-85 (Frest 1987) 6 1998-99 (Arbuckle et al. 2000) 0 -6 -100% Evaluated Not 5b 2012 (Iowa DNR WIS) 1 As presented by Arbuckle et al. (2000), the potential causes of
declines in species richness of Iowa's freshwater mussels include siltation,
destabilization of stream substrate, stream flow instability, and high
instream levels of nutrients (phosphorus and nitrogen). Their study also
suggested the importance of stream shading provided by riparian vegetation to
mussel species richness. Class BWW1 – Fish Kill
Assessment: BioNet Site ID Date Drainage Area (mi2) Ecoregion Major Drainage/
Thermal Fish per mile 52b REMAP 25 % fish
per mile >52b REMAP 25 %
fish per mile? 52b expected fish
taxa Fish Taxa Present %
(>50% to pass) 1411 8/12/2024 516 52b MS/WW 2513 575 Yes (Pass) 10/14 71% (Pass) The Class BWW1 use previously resided in
Category 3b based on a 2023 fish kill. The results of a 2024 fish sample
showed the fish community recovered and is similar to non-fish kill impacted
streams in the ecoregion. According to updated IR methodology for large river
fish kill follow-up, the category for the fish kill assessment was changed
from 3b to 3a (not assessed).
Details about the 2023 fish kill can be found here: https://programs.iowadnr.gov/fishkill/events/1043 Site ID Biopart Year Species # in sample / # of
samples Avg Length (cm) (Avg) Hg (ppm) Chlordane (ppm) Sum PCBs (ppm) 1094 whole 2023 common carp 3 51.8 0.13 <0.05 J0.0313 Support Level Not A historic one meal/week mercury consumption
advisory existed on this segment. Based on IR Methodology, the Class HH (fish
consumption) use remains assessed as “not supported.”
Class A1 - Indicator Bacteria: 2012-2014
Class BWW1 - Biological Sampling:
Overall:
Class BWW1 – Freshwater Mussel Sampling:
Class HH - Fish Tissue Sampling: