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Iowa’s Section 303(d) Impaired Waters Listings

Under Section 303(d) of the Clean Water Act, states are required from "time to time" to submit a list of waters for which effluent limits will not be sufficient to meet all state water quality standards. EPA has defined "time to time" to mean April 1 of even numbered years. The failure to meet water quality standards might be due to an individual pollutant, multiple pollutants, "pollution," or an unknown cause of impairment. The 303(d) listing process includes waters impaired by point sources and non-point sources of pollutants. States must also establish a priority ranking for the listed waters, taking into account the severity of pollution and uses. The EPA regulations that govern 303(d) listing can be found in the Code of Federal Regulations 40 CFR 130.7.

The Iowa Department of Natural Resources TMDL and Water Quality Assessment Section compiles this impaired water list, or 303(d) listing. The 303(d) listing is composed of those lakes, wetlands, streams, rivers, and portions of rivers that do not meet all state water quality standards. These are considered "impaired waterbodies" and states are required to calculate total maximum daily loads (TMDLs) for pollutants causing impairments.

Additional Resources

Draft 2014 Impaired Waters List: Request for Public Comments

Iowa DNR has prepared a draft 2014 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 2014 draft Integrated Report. Iowa DNR is now seeking public comments on this draft list. Public comments will be solicited from May 19, 2015 through July 2, 2015. 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: John Olson
Water Quality Monitoring & Assessment Section
Wallace State Office Building
502 East 9th Street
Des Moines, IA 50319

Comments can also be e-mailed to John Olson at the following address:


Iowa’s draft 2014 Section 303(d) list of impaired waters was prepared according to U.S. EPA guidelines for “integrated reporting” that combines requirements of Sections 305(b), 303(d), and 314 of the federal Clean Water Act.  These guidelines suggest that states place all their waters into one of five categories of their Integrated Report:

  • Category 1: All designated uses* are met.
  • Category 2: Some of the designated uses are met but insufficient information exists to determine whether the remaining uses are met.
  • Category 3: Insufficient information exists to determine whether any designated uses are met.
  • Category 4: The waterbody is impaired but a TMDL is not required.
  • Category 5: The waterbody is impaired and a total maximum daily load (TMDL) is needed (Category 5 is the state’s Section 303(d) list).

[*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.]

Iowa’s 2014 Section 303(d) list is the seventh to be developed under Iowa’s Credible Data Law. This law requires that listing decisions be based on scientifically valid chemical, physical, or biological data collected under a scientifically accepted sampling and analysis plan, including quality control and quality assurance procedures.  The Department believes that this law has been implemented in conjunction with the federal listing requirements such that all readily available and existing water quality related data and information have been used for list development.

Iowa's draft 2014 Section 303(d) list (Category 5 of the Integrated Report) contains 572 waterbodies with a total of 751 impairments  There were 480 waterbodies on Iowa’s 2012 final EPA-approved list and 474 waterbodies on the 2010 list. 

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) 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.  Iowa’s draft 2014 list of waters in need of further investigation contains 358 waterbodies.  Of the 363 waterbodies on the final 2012 WINOFI list, a total of 42 waterbodies were moved to other categories of the integrated report as follows:

  • New data at 12 waterbodies showed that an impairment did not exist; thus, these waterbodies were moved to IR Category 2a (at least one use assessed as fully supporting designated uses)
  • Twenty-one fish kill waterbodies where IDNR brought legal action and fines against responsible parties were moved to IR Category 3a (uses not assessed.)
  • New data showed that nine waterbodies should, in fact, be assessed as "impaired", and these waters were placed in Category 5 (=Section 303(d) list).

The following materials are presented for review:

All of Iowa’s Section 305(b) water quality assessments developed since 1992 are available at Iowa DNR’s on-line water quality assessment database, ADBNet