Shell Rock River IA 02-SHL-783
from south corporate limit of Shell Rock (S12 T91N R15W Butler Co.) to confluence with Flood Cr. in S27 T93N R16W Butler Co.
- Cycle
- 2026
- Current Phase
- Public Comment
- Overall IR
- 5 - Water is impaired or threatened and a TMDL is needed.
- Trend
- Improving
- Trend Comment
- Presumptive Class A1 indicator bacteria impairment was delisted.
- Created
- 10/27/2025 3:09:38 PM
- Updated
- 1/12/2026 3:02:48 PM
| Cycle Added | Class | Cause | Data Source | Rationale |
|---|---|---|---|---|
| 2018 | Class A1 | Bacteria: Indicator Bacteria- E. coli | Ambient monitoring: Iowa DNR-rivers | New data: WQ improvement (chemical / physical / bacterial) |
The Class A1 use was assessed as "fully supported" based on indicator bacteria (E. coli) and pH monitoring data. The previous Category 5p Class A1 indicator bacteria impairment was delisted. The Class BWW1 use was assessed as "fully supported" based on biological sampling data and water quality monitoring data. The Class HH use remains assessed as "not supported" based on fish tissue sampling data and due to the historic existence of a one meal/week mercury consumption advisory in this segment.
Data Sources: Data Source Data Source ID Data Type Data Age Site ID Site
Name Site
Description Iowa DNR 6 WQ CY 2022-2024 10120001 Shell
Rock River at Shell Rock
Iowa DNR 6 BIO See Below 843 Shell
Rock River Shell
Rock Iowa DNR 6 BIO See Below 1319 Shell
Rock River Clarksville
(REMAP #272) Iowa DNR 6 FT See Below 1068 Shell
Rock River W of
Clarksville Site ID Data Source ID # Samples per Year (2022/ 2023/2024) 2022 Geometric Mean 2023 Geometric Mean 2024 Geometric Mean Violates Annual Geometric Mean? # 2022 SSM violations / SSM Violations needed for impairment # 2023 SSM violations / SSM Violations needed for impairment # 2024 SSM violations / SSM Violations needed for impairment Violates Annual SSM Significantly >10% Rule? Assessment Type Support Level 10120001 6 8/8/8 82 39 71 NO 1 / 3 0 / 3 1 / 3 NO MONITORED FULL 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 10120001 6 35 / 3 7.9 8.9 8.3 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 10120001 6 Chloride 36 / 3 18 39 26 NA 0 / 0 7 NO MONITORED FULL 10120001 6 Dissolved Oxygen 35 / 3 7.4 14.5 11.2 0 NA / NA 7 NO MONITORED FULL 10120001 6 pH 35 / 3 7.9 8.9 8.3 0 NA / NA 7 NO MONITORED FULL 10120001 6 Sulfate 36 / 3 24 110 42 0 NA / NA 7 NO MONITORED FULL 10120001 6 Temperature 36 / 3 0 24.4 11.5 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 10120001 6 Aluminum 18 / 2 1400 296 165 0 / 1 NO MONITORED FULL 10120001 6 Ammonia 35 / 3 0.2 0.04 0.02 0 / 0 NO MONITORED FULL 10120001 6 Cadmium 18 / 2 0.5 0.5 0.5 0 / 0 NO MONITORED FULL 10120001 6 Chromium 18 / 2 2 0.7 0.5 0 / 0 NO MONITORED FULL 10120001 6 Copper 18 / 2 1.6 0.8 0.5 0 / 0 NO MONITORED FULL 10120001 6 Lead 18 / 2 1 1 1 0 / 0 NO MONITORED FULL 10120001 6 Nickel 18 / 2 4.2 1.3 1.2 0 / 0 NO MONITORED FULL 10120001 6 Selenium 36 / 3 2.6 1 1 0 / 0 NO MONITORED FULL 10120001 6 Silver 18 / 2 1 1 1 0 / 0 NO MONITORED FULL 10120001 6 Zinc 18 / 2 1.5 0.7 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 47c BMIBI BIT BMIBI Pass/Fail 843 8/15/22 1730.2 47c MS Hess 82 Excellent 70 Pass 1319 9/21/21 1630.0 47c MS Hess 63 Good 70 Fail 843 8/23/19 1730.2 47c MS Hess 72 Good 70 Pass 843 8/20/19 1730.2 47c MS Hess 58 Good 70 Fail 843 8/15/16 1730 47c MS Hess 81 Excellent 70 Pass BioNet Site ID Date Drainage Area (mi2) Ecoregion Major Drainage/Thermal Riffle Stream? FIBI score FIBI Class 47c FIBI BIT FIBI Pass/Fail 1319 9/21/21 1630.0 47c MS Und. 82 Excellent 44/65 Pass Community Assessment Type Assessment Result Support Level IR Category Reason Benthic Macroinvertebrates Evaluated Pass (3/5) Full Fish Evaluated Pass (1/1) Full Assessment was
evaluated because the drainage areas of the sites Overall Evaluated Pass Full 1 used for the assessment were
greater than the calibrated range. Site ID Data Source ID # Days Monitoring (2016) DO Criteria Type # 2016 violations / Violations needed for impairment Violates Annual Significantly >10% Rule? Assessment Type Support Level 24 hr 1/6 No 843 6 29 16 hr 0/6 No Evaluated Full Site ID Biopart Year Species # in sample / # of samples Avg Length (cm) (Avg) Hg (ppm) Chlordane (ppm) Sum PCBs (ppm) 1068 tissue plug 2012 walleye 3 40.0 0.285 1068 tissue plug 2011 walleye 4 47.2 0.753 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.” 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 10120001 6 Copper 18 / 2 1.6 0.8 0.5 12 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 10120001 6 Selenium 12/12/12 0.917 0.808 1.358 4/5/3 FS/FS/FS MONITORED FULL
Class A1 - Indicator Bacteria:
Class A1 – pH:
Class BWW1 - Binomial Parameters:
Class BWW1 - Toxic Parameters:
Class BWW1 - Biological Sampling:
Fish:
Overall:
Class BWW1 - Continuous DO Monitoring:
Class HH - Fish Tissue Sampling:
Class HH-F - Toxic Parameters: