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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

2012 Impaired Waters List

Iowa DNR submitted its final 2012 Integrated Report, including Iowa's 2012 list of impaired waters, to U.S. EPA for approval on March 25, 2013. Iowa DNR received final approval of this submittal from U.S. EPA on April 24, 2013.

Public comments were sought on Iowa’s draft 2012 list from January 15, 2013 through February 28, 2013. Comments were submitted to IDNR by one government agency (U.S. EPA) and one environmental group. Iowa DNR prepared a summary of responses to these comments.  Changes were made to the draft list based on the comments received. Iowa's final 2012 Section 303(d) list, as submitted to U.S. EPA on March 25, 2013, for review and approval, contained 480 waterbodies with a total of 642 impairments. This version of the list was approved by U.S. EPA on April 24, 2013.

All states submit their Integrated Report and list of impaired waters every two years as required by Sections 305(b) and 303(d) of the Clean Water Act. Iowa’s 2012 Integrated Report was prepared according to U.S. EPA guidelines that combine (integrate) requirements of Sections 305(b), 303(d), and 314 of the federal Clean Water Act. These guidelines suggest that states place all their waters (lakes, wetlands, streams, and rivers) into one of five general categories of their Integrated Report:
  • Category 1: All designated uses (e.g., for water contact recreation, aquatic life, and/or drinking water) 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 uses are met.
  • Category 4: The waterbody is impaired but a total maximum daily load (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 of impaired waters

Iowa’s 2012 Section 303(d) list (Category 5 of the Integrated Report) is the sixth such list to be developed under Iowa's Credible Data Law. This law, passed by the Iowa Legislature in 2000, 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 this “credible data” 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.

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, that a water quality impairment exists. 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 final 2012 list of waters in need of further investigation (WINOFI) contains 340 waterbodies.  Iowa’s previous (2010) list of waters in need of further investigation contained 254 waterbodies. While 219 of the waterbodies from the 2010 WINOFI remain on Iowa’s 2012 “further investigation” list, 35 waterbodies were moved to other categories of the 2012 Integrated Report as follows:

  • New data at sixteen 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).
  • Nine 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 six waterbodies identified as “potentially impaired” should, in fact, be assessed as “impaired”, and these waters were placed in Category 5 (=Section 303(d) list).
  • Three waterbodies were removed due to assessment errors that mistakenly suggested potential impairment.
  • One waterbody was removed due to lack of recent water quality data.

The following materials comprise Iowa's final 2012 Integrated Report that was approved by U.S. EPA on April 24, 2013. The Section 303(d) list (Category 5) is the only EPA-approvable part of the Integrated Report.


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