Iowa's Section 303(d) Impaired Waters List
Under Section 303(d) of the Clean Water Act, states, tribes, and territories 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 source and non-point source 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) list. The 303(d) list includes 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 the impairments.
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 DNR 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 DNR 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.
Iowa's Integrated Report
Iowa’s Integrated Report (IR) is 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. The impaired waters list, along with lists of waters in other categories of the IR, can be found in Iowa's water quality assessment database, ADBNet. This database contains water quality assessments for each waterbody segment and also provides summary information for the impaired waters lists and IRs. An interactive map of all impaired water segments is also available on the ADBNet website.