Iowa DNR

Water Quality Assessments

Impaired Waters List

2020 305(b) Assessment Summary

DRAFT 2020 Impaired Waters List: request for public comments:

Iowa DNR has prepared a draft 2020 list of impaired waters as required by Section 303(d) of the federal Clean Water Act. This list is also known as "Category 5" of Iowa's 2020 Integrated Report. Iowa DNR is now seeking public comments on this draft list. Public comments will be solicited from December 1, 2020, through January 1, 2021. Following the end of the public comment period, the draft list will be modified based on the comments received, and the revised list will be forwarded to U.S. EPA for their review and approval or disapproval. Please mail comments to:

Iowa Department of Natural Resources
Attention: IR Comments
Water Quality Monitoring & Assessment Section
Wallace State Office Building
502 East 9th Street
Des Moines, IA 50319

Comments can also be e-mailed to Iowa DNR at the following

Materials for review

Iowa's draft 2020 list of Section 303(d) impaired waters (Category 5 of the Integrated Report). The list contains 586 waterbodies with a total of 775 impairments. There were 622 waterbodies with 831 impairments on Iowa's 2018 final EPA-approved list.Iowa's draft 2020 Methodology and links to additional materials for review can be found on the Publications page.


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. These U.S. EPA guidelines suggest that states place all their waters into one of the following categories that comprise a state's Integrated Report:

  • Supporting: These waterbodies are assessed as fully supporting their assessed designated uses*. Waters assessed as supporting all their designated uses are in Category 1 of the Integrated Report. Those waters where some of the designated uses are met but insufficient information exists to determine whether the remaining uses are met are placed in Category 2 of the Integrated Report.
  • Uses Not Assessed: These are designated uses for which insufficient information exists to determine whether that designated use is met. Other designated uses for that waterbody, however, may have been assessed as either "supporting" or "impaired".
  • Waterbodies Not Assessed: Insufficient information exists to determine whether any beneficial uses designated for that waterbody are met. These waterbodies are placed into Category 3 of the Integrated Report.
  • Category 4: The waterbody is impaired but a TMDL is not required; the waterbody is not included on the state's section 303(d) list of impaired waters (Category 5 of the Integrated Report).
  • Category 5: The states Section 303(d) list of impaired waters. The waterbody is impaired and a total maximum daily load (TMDL) is needed.
  • 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. As specified in the credible data law, this list is not part of the Section 303(d)/impaired waters process in Iowa and includes waterbodies 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 waterbody can be added to Iowa's Section 303(d) list.
  • Delistings: These waters are proposed for removal from Iowa's previous (2018) list of impaired waters. A rationale for each proposed delisting is provided.

[*Designated uses are beneficial uses applied to specific Iowa surface waters (streams, rivers, lakes, and wetlands) in the Iowa Water Quality Standards. Examples of beneficial uses are uses for primary contact recreation (for example, swimming-type uses), aquatic life protection, and as a source of water for a public water supply. Beneficial uses designated for Iowa's surface waters are protected by narrative and numeric water quality criteria. For a more 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. For a list of the Iowa surface waters and their respective designated uses, see Iowa's Surface Water Classification.]

Assessment Results

Waterbodies that Fully meet WQ standards are those that are in Integrated Report Categories 1 and 2. Potentially impaired waters are placed on Iowa's list of Waters in Need of Further Investigation (WINOFI), and Impaired waterbodies include all those in Integrated Report Categories 4 and 5.

The number of assessments the Iowa DNR can make in a given cycle are limited by budgets and staffing resources. The following charts show the proportions to which each waterbody type meets WQ standards, and the percentage that has been assessed in this cycle.

Rivers and Streams
Lakes and Reservoirs

Summary Statistics

These charts will render best if you change your device's orientation to landscape.

Category 5 Impaired Waters List

Total number of impaired waterbody segments
Total number of impaired uses

Overall Integrated Report Categories

Category - Description Waterbody Segments
1 - All designated uses are met. 16
2 - Some of the designated uses are met but there is insufficient data to determine if remaining designated uses are met. 268
3 - Insufficient data exist to determine whether any designated uses are met. 1546
4 - Water is impaired or threatened and a TMDL has been completed or is not needed. 166
5 - Water is impaired or threatened and a TMDL is needed. 584
TMDL information and documentation for finalized TMDLs can be found at Iowa DNR Water Improvement Plans