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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 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.
2016 Impaired Waters List and Integrated Report
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 2014 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 waters (lakes, wetlands, 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
2016 Section 303(d) list (Category 5 of the Integrated Report) is the eighth
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.
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 2016 list of waters in need of further investigation
(WINOFI) contains 476 waterbodies with 531 potential impairments.