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 Water Quality Monitoring and 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.

2022 Integrated Report including the 2022 Impaired Waters List: Approved by US EPA on April 29, 2022

This list, along with lists of waters in other Categories of the Integrated Report, can be found in Iowa's water quality assessment database, ADBNet. This database contains a site location map and a water quality assessment for each individual impaired segment. The database also provides summary information for the 2022 list of impaired waters and Integrated Report (charts and graphs). An interactive map of all impaired water segments is available on the ADBNet website.

Iowa’s Integrated Report and list were 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 water segments (lakes, 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 required.

Category 5 is the state’s Section 303(d) list of impaired waters

The Section 303(d) list (Category 5 of the Integrated Report) is 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 waterbody segments where limited information suggests, but does not 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 segment can be added to Iowa's Section 303(d) list.

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