Iowa DNR

Water Quality Assessments

Impaired Waters List

2020 305(b) Assessment Summary

2020 Integrated Report including the 2020 Impaired Waters List: Approved by U.S. EPA on May 14, 2021:

Iowa DNR submitted the 2020 Integrated Report which includes the 2020 Impaired Waters List to the U.S. EPA as required by Sections 305(b) and 303(d) of the federal Clean Water Act for approval on February 17, 2021. Iowa DNR received final approval of this submittal from the U.S. EPA on May 14, 2021

Public comments were sought on Iowa’s draft 2020 list of impaired waters from December 1, 2020, through January 1, 2021. Iowa DNR prepared a summary of responses to the 112 comments received on the draft 2020 list of Impaired Waters Iowa’s draft list was updated following the public comment period and Iowa's final 2020 Impaired Waters list, as submitted to U.S. EPA, contained 584 waterbodies with a total of 773 impairments.

Materials for review

    Links to additional background information can be found at:


    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. 15
    2 - Some of the designated uses are met but there is insufficient data to determine if remaining designated uses are met. 271
    3 - Insufficient data exist to determine whether any designated uses are met. 1542
    4 - Water is impaired or threatened and a TMDL has been completed or is not needed. 167
    5 - Water is impaired or threatened and a TMDL is needed. 585
    TMDL information and documentation for finalized TMDLs can be found at Iowa DNR Water Improvement Plans