2024 305(b) Assessment Summary
2024 Integrated Report including the 2024 Impaired Waters List:
Iowa DNR (DNR) sought public comments on Iowa’s draft 2024 Integrated Report (IR), including the list of impaired waters, from March 14, 2024 through April 12, 2024. The DNR prepared a summary of responses to the seven comments received on the draft IR. The DNR submitted the draft IR which included the 2024 Impaired Waters List that contained 577 water bodies with a total of 746 impairments to the U.S. EPA Region VII (EPA R7) for approval on May 9, 2024 as required by Sections 305(b), 303(d), and 314 of the federal Clean Water Act. The DNR received a partially approving / partially disapproving decision document for Iowa’s 2024 Clean Water Act Section 303(d) list from the EPA R7 on November 12, 2024. EPA R7 added seven impairment to Iowa’s 303(d) list after seeking public comment from November 13, 2024 to December 13, 2024. EPA R7 provided the "2024 Response to Comments for EPA’s Partial Approval / Partial Disapproval of Iowa’s Clean Water Act Section 303(d) List of Water Quality Limited Segments Still Requiring TMDLs" document to the DNR on December 30, 2024. The DNR received a Rescission and Reconsideration letter of EPA R7’s partial disapproval of Iowa’s 2024 Section 303(d) list and Identification of Waters from the EPA R7 on July 11, 2025. This letter only rescinds the seven impairments added to Iowa’s 303(d) list in the December 30, 2024 decision document.
The draft IR methodology and assessments are released for public review. The public has 30 days to comment on the IR methodology, data, or the assessments during this period.
The Iowa draft Integrated Report is submitted to US EPA Region 7 for review and approval.
The USEPA Region 7 has reviewed the Iowa submission and responded with a decision document. The Iowa DNR assessment summary page for this cycle will contain details regarding the EPA response.
The Integrated Report has been approved and finalized.
Documentation
Iowa's Section 303(d) lists and Integrated Reports are prepared according to Iowa DNR's assessment and listing methodology and follow U.S. EPA guidelines for "integrated reporting" that combine requirements of Sections 305(b), 303(d), and 314 of the federal Clean Water Act.
The final methodology used for this assessment cycle can be downloaded from the State Library of Iowa - Iowa Publications Online website.
For a detailed description of designated uses applied to Iowa surface waters, see pages 9 and 10 [Surface Water Quality Criteria, Designated Use Segments] of the Iowa Water Quality Standards. This cycle's assessment unit designated uses are based on this version of the Surface Water Classification document.
All documentation submitted to and received by the US EPA in regards to this cycle can be found on the US EPA ATTAINS website:
| Agency | Document | Document Type |
|---|
Designated Uses and Assessment Categories
Each assessment unit has one or more Designated Uses. Beneficial uses designated for Iowa's surface waters are protected by narrative and numeric water quality criteria. A waterbody may be supporting one or more uses, but if a single parameter or analyte that fails to meet the criteria for a use (such as low dissolved oxygen or a low fish biotic index score) can result in that waterbody being placed on the Impaired Waters List. The U.S. EPA guidelines suggest that states place all their waters into one of the following categories that comprise a state's Integrated Report.
Supported Waters
Supported waters are those segments in Integrated Report Categories 1 and 2.
- Category 1: All designated uses are met
- Category 2: One or more designated uses are met, but there are insufficient data to determine if the remaining designated uses are met.
Waters In Need of Further Investigation (WINOFI)
As provided for in Iowa's Credible Data Law, the Department is to maintain a separate list of waters that require further investigative monitoring. This list is not part of the Section 303(d)/impaired waters process in Iowa and includes segments where limited information suggests, but does not conclusively (credibly) demonstrate, a water quality impairment. If the results of further investigative monitoring demonstrate, with data of sufficient quality and quantity, that a water quality impairment exists, the affected segment can be added to Iowa's Section 303(d) list.
Impaired Waters
Impaired waters are those segments in Integrated Report Categories 4 and 5.
- Category 4: The segment is impaired but a TMDL is not required; the segment is not included on the state's section 303(d) list of impaired waters (Category 5 of the Integrated Report).
- Category 5: Iowa's Section 303(d) List of Impaired Waters. The segment is impaired and a total maximum daily load (TMDL) is needed.
Not Assessed
The number of assessments the Iowa DNR can make in a given cycle are limited by budgets and staffing resources.
- Category 3: Insufficient data to determine whether any designated uses are met.
Assessment Results
Overall Integrated Report Categories
| Category - Description | Waterbody Segments |
|---|---|
| 1 -- All designated uses are met. | 24 |
| 2 -- Some of the designated uses are met but there is insufficient data to determine if remaining designated uses are met. | 362 |
3 -- Insufficient data exist to determine whether any designated uses are met.
EPA Category 3 and WINOFIsIowa maintains a separate list, per the Credible Data Law, of segments with insufficient information (WINOFI). Because these segments do not have enough information to determine use support, EPA considers these "Not Assessed". Therefore, for the purpose of reporting the Integrated Report to EPA, these WINOFI segments are grouped into the EPA's Category 3. For this cycle, there are a total of 321 WINOFI segments and 1324 "Not Assessed" segments. |
1645 |
| 4 -- Water is impaired or threatened and a TMDL has been completed or is not needed. | 145 |
| 5 -- Water is impaired or threatened and a TMDL is needed. | 577 |
Summary Statistics
TMDL information can be found at Iowa DNR Water Improvement Plans
Finalized TMDLs and the assessment units they apply to can be viewed at the Water Quality Improvement Plans/TMDLs codex page.