South Skunk River IA 03-SSK-934
from the Ames Water Works dam in River Valley Park at Ames (S36 T84N R24W Story Co.) to the Co. Rd. at north line of S6 T85 R23W Story Co (approximately 1 mile NNE of Story City)
- 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 3:09:40 PM
- Updated
- 11/24/2025 2:17:06 PM
The Class A1 use remains assessed as “not supported” due to levels of indicator bacteria that violated state water quality criteria. The Class BWW1 use remains assessed as "not supported" based on biological 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 WQ CY 2012-2014 10850003 South
Skunk River Upstream
of Ames (US1) Iowa DNR 6 BIO See Below 38 South
Skunk River Ames Iowa DNR 6 BIO See Below 1540 South
Skunk River Oheim
Prairie - Story City Story Co. 26 WQ CY 2022-2024 99990168 South
Skunk River Site
monitored by Prairie River Watershed Group and Story Co. Conservation Story Co. 26 WQ CY 2022-2022 99990169 South
Skunk River Site
monitored by Prairie River Watershed Group and Story Co. Conservation Story Co. 26 WQ CY 2022-2022 99990201 South
Skunk River Site
monitored by Prairie River Watershed Group and Story Co. Conservation Class A1 - Indicator Bacteria: 2012-2014 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 10850003 6 22 /
3 46 94 223 Yes 7 32% Yes EVALUATED NOT Class A1 - Indicator
Bacteria: 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 99990168 26 8/9/8 131 98 339 YES 1 / 3 4 / 3 3 / 3 YES EVALUATED WINOFI 99990169 26 8/9/8 176 377 324 YES 4 / 3 4 / 3 4 / 3 YES EVALUATED WINOFI 99990201 26 7/9/7 162 149 255 YES 3 / 3 5 / 3 4 / 3 YES EVALUATED WINOFI The
bacteria samples were collected by the Prairie Rivers Watershed Group and
Story County Conservation with the analyses conducted by the City of Ames.
Since the data were not collected under a DNR-approved quality assurance
plan, the assessment was considered "evaluated" instead of
"monitored." According to Iowa DNR’s assessment/listing
methodology, impairments based on “evaluated” assessments are of lesser
confidence and are not appropriate for Section 303(d) listing (Category 5 of
the Integrated Report). The Iowa DNR does, however, consider these assessments
appropriate for listing under Category 3b of the Integrated Report (waters
potentially impaired and in need of further investigation). Class BWW1 -
Biological Sampling: BioNet Site ID Date Drainage Area (mi2) Ecoregion Major Drainage/Thermal BM Sample Gear BMIBI score BMIBI Class 47b BMIBI BIT BMIBI Pass/Fail 1540 9/12/24 180.0 47b MS/WW Surber 59 Good 62 Fail 38 9/19/22 254.3 47b MS/WW Surber 55 Good 62 Fail BioNet Site ID Date Drainage Area (mi2) Ecoregion Major Drainage/Thermal Riffle Stream? FIBI score FIBI Class 47b FIBI BIT FIBI Pass/Fail 1540 9/12/24 180.0 47b MS/WW Yes 48 Good 53 Fail 38 9/19/22 254.3 47b MS/WW No 39 Fair 32 Pass Community Assessment Type Assessment Result Support Level IR Category Reason Benthic Macroinvertebrates Monitored Fail (0/2) Not Fish Evaluated Fail (1/2) WINOFI Assessment was monitored
because the samples used for the Overall Monitored Fail Not 5bv the assessment were collected
in a recent five year period.
Benthic Macroinvertebrates:
Fish:
Overall:
Class HH - No Data