Shell Rock River IA 02-SHL-787
from confluence with Rose Cr. (NW 1/4 S8 T97N R19W Cerro Gordo Co.) to the Iowa/Minnesota state 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 3:09:55 PM
- Updated
- 1/13/2026 6:57:12 AM
The Class A1 use remains assessed as “not supported” based on indicator bacteria monitoring. The Class BWW1 use was assessed as “WINOFI” based on continuous dissolved oxygen monitoring data. The Class HH (fish consumption) use was assessed as "fully supported" based on fish tissue sampling data. Note: A TMDL for the bacteria impairment in the Cedar River basin was prepared and was approved by EPA in February 2010. However, this segment was not included in the TMDL; therefore, the bacteria impairment of the Class A1 primary contact recreation use for this segment remains in IR Category 5a (TMDL needed).
Data Sources: Data Source Data Source ID Data Type Data Age Site ID Site
Name Site
Description Iowa DNR 6 WQ CY 2022 14000351 Shell
Rock River
Iowa DNR 6 BIO See Below 331 Shell
Rock River Kensett
– REMAP #23 Iowa DNR 6 FT See Below 1109 Shell
Rock River S of
Northwood Site ID Data Source ID # Samples per Year (2022) 2022 Geometric Mean Violates Annual Geometric Mean? # 2022 SSM violations / SSM Violations needed for impairment Violates Annual SSM Significantly >10% Rule? Assessment Type Support Level 14000351 6 6 118 NO 1 / NA NO EVALUATED FULL Even though the indicator bacteria sampling data shows full support, a "fully supported" monitored assessment is needed to de-list the impairment. 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 14000351 6 6 / 1 7.81 8.45 8.14 0 3 NO EVALUATED 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 14000351 6 Dissolved Oxygen 6 / 1 9.64 11.37 10.46 0 NA / NA 3 NO EVALUATED FULL 14000351 6 pH 6 / 1 7.81 8.45 8.14 0 NA / NA 3 NO EVALUATED FULL 14000351 6 Temperature 6 / 1 4.969 25.381 18.82 0 NA / NA 3 NO EVALUATED FULL Site ID Date Drainage Area (mi2) Ecoregion Major Drainage BM Sample Gear BMIBI score BMIBI Class 47c BMIBI BIT BMIBI Pass/Fail 331 9/17/20 306.4 47c MS Floating Art Sub 50 Fair 52 Pass* Site ID Date Drainage Area (mi2) Ecoregion Major Drainage Riffle Stream? FIBI score FIBI Class 47c FIBI BIT FIBI Pass/Fail 331 9/17/20 306.4 47c MS Yes 68 Good 65 Pass Community Assessment Type Assessment Result Support Level IR Category Reason Benthic Macroinvertebrates Evaluated Pass (1/1) Full *BMIBI passed using
8 pt. BMIBI UAV applied to single samples. Fish Evaluated Pass (1/1) Full Overall Evaluated Pass Full 1 Assessment was evaluated because it was
based on a single sample. Site ID Data Source ID # Days Monitoring (2020) DO Criteria Type # 2020 violations / Violations needed for impairment Violates Annual Significantly >10% Rule? Assessment Type Support Level 24 hr 6/5 Yes 331 6 21 16 hr 1/5 No Evaluated WINOFI Site ID Biopart Year Species # in sample / # of samples Avg Length (cm) (Avg) Hg (ppm) Chlordane (ppm) Sum PCBs (ppm) 1109 fillet 2015 common carp 5 46.6 0.19 0.02 0.06 1109 tissue plug 2015 walleye 5 44.5 0.218 Support Level Full
Class A1 - Indicator Bacteria:
Class A1 – pH:
Class BWW1 - Binomial Parameters:
Benthic
Macroinvertebrates:
Fish:
Overall:
Class BWW1- Continuous DO Monitoring:
Class HH - Fish Tissue Sampling: