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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.
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. The ADBNet database also provides summary information for the 2020 list of impaired waters and Integrated Report (charts and graphs). An interactive map of all draft 2020 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 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.