Skip to content
EPA Environmental Dataset Gateway
EPA Office of Water (OW): Impaired Waters with TMDLs by Causes of Impairment and Probable Sources and TMDL Pollutant
US Environmental Protection Agency, Office of Water
Under Section 303(d) of the Clean Water Act (CWA), states, territories, and authorized tribes, collectively referred to in the Act and here as "states," are required to develop lists of impaired waters. A state’s 303(d) impaired waters list is comprised of all waters where required pollution controls are not sufficient to attain or maintain applicable water quality standards. The law requires that states establish priority rankings for waters on the lists and develop Total Maximum Daily Loads (TMDLs). A TMDL is a calculation of the maximum amount of a pollutant that a waterbody can receive and still meet water quality standards, and an allocation of the load reduction needed from various sources of the pollutant.
The data can be used to identify the distribution of impaired waters with a TMDL within each state for pollutants of interest. The attribute information provided (e.g., TMDL pollutant, location, waterbody name) can be associated with the geospatial information (TMDLs on Impaired Waters NHD Indexed Dataset found at
). The attribute information can be viewed via ATTAINS available at
or downloaded via the AskWATERS Expert Query available at
. Please note that a water can be identified on a State’s 303(d) list as impaired for more than one cause of impairment and be identified as having more than one probable source. EPA considers TMDLs as water/pollutant combinations, please be mindful of this information when aggregating the attributes for analysis needs.
Time Period of Content
West Bounding Longitude:
East Bounding Longitude:
North Bounding Latitude:
South Bounding Latitude:
Please confirm that you are using the most recent copy of both data and metadata. Acknowledgement of the EPA would be appreciated.
impaired waters, 303d, TMDL, clean water act, listed waters, total maximum daily loads, TMDLs, CWA, point source, EPA, Stream, reach
Although these data have been processed successfully on a computer system at the Environmental Protection Agency, no warranty expressed or implied is made regarding the accuracy or utility of the data on any other system or for general or scientific purposes, nor shall the act of distribution constitute any such warranty. It is strongly recommended that careful attention be paid to the contents of the metadata file associated with these data to evaluate data set limitations, restrictions or intended use. The U.S. Environmental Protection Agency shall not be held liable for improper or incorrect use of the data described and/or contained herein.
Metadata Reference Information
Metadata Standard Name:
FGDC Content Standards for Digital Geospatial Metadata
Metadata Standard Version:
The EDG is a metadata portal that is part of
EPA's System of Registries
. Please read EPA's
Privacy and Security Notice
Access EPA's National Geospatial Home Page
Access EPA's Intranet Geospatial Home Page