This map shows lakes, estuaries, rivers, and coastlines that have been designated as impaired under Section 303(d) of the Clean Water Act. It also shows water bodies which were at one time listed on the 303(d) list but now have total maximum daily loads (TMDL) established to improve water quality. The Clean Water Act requires states to identify water bodies where existing pollution controls are not sufficient to meet water quality standards; water bodies that fail to meet these standards are required to establish a TMDL in order to address the cause of impairment. Water bodies may be impaired for more than one pollutant, and each pollutant requires its own TMDL. The objective of a TMDL is to design an implementation plan to restore impaired water bodies. Once a TMDL is established the water body is removed from the 303(d) listing and placed in the TMDL database. Water bodies with multiple causes of impairment can be found in both the 303(d) and the TMDL list.

Impaired waters and TMDL features appear on the map only when zoomed in on a small geographic area. Users can click on a watershed to zoom in to its impaired waters and TMDLs, and then click on a feature to view a detailed report.

Purple lines on the map indicate the boundaries of watersheds and subwatersheds based on Hydrologic Unit Codes (HUC).

Data Considerations

The impaired waters and TMDL features shown on this map are based on a data service (last updated in February 2014) hosted by the Environmental Protection Agency (EPA). The 303(d) list of impaired waters shows those waters that are impaired or threatened by a pollutant and are in need of a Total Daily Maximum Load (TMDL). The TMDL list shows waters that were once part of the 303(d) impaired waters list but were removed once a TMDL was established for the pollutant. If the water body has multiple causes of impairment and only one TMDL is established, then that feature will appear on both the 303(d) and TMDL list.

The 303(d) list of impaired waters does not include (a) impaired waters for which an EPA-approved TMDL has already been established, (b) impaired waters for which other pollution-control mechanisms are in place and expected to attain water quality standards, or (c) waters impaired as a result of something other than a pollutant (e.g. invasive species).

Links to detailed reports, hosted on the EPA Waterbody Quality Assessment Report website, are provided pop-up boxes for each feature. Users must zoom to a scale of 1:288,895 in order to view the features. Watershed areas are from Natural Resources Conservation Service (NRCS) data for HUC-6, HUC-8, HUC-10 and HUC-12 boundaries. Labels with watershed names are visible only at the 6-digit level. The service is a tile cache that is visible at scales smaller than 1:144,448.



The data will be updated as EPA pushes out changes to its web services.