An official website of the United States government.

This is not the current EPA website. To navigate to the current EPA website, please go to This website is historical material reflecting the EPA website as it existed on January 19, 2021. This website is no longer updated and links to external websites and some internal pages may not work. More information »

National Pollutant Discharge Elimination System (NPDES)

EPA's Stormwater Discharge Mapping Tools

The discharge mapping tool can help you determine:

  • the receiving waters to which your facility discharges, and
  • whether they are considered "impaired" under section 303(d) of the Clean Water Act.

The discharge mapping tool uses the National Hydrologic Dataset Plus (NHDPlus) catchment data layer and NHD waters indexed with section 303(d) listing and total maximum daily load (TMDL) information to analyze whether a project is located with the catchment of an impaired water, and therefore discharges to that impaired water.

You also can use the tool to assist you in providing the required receiving waters information on your Notice of Intent (NOI) for the:

Using the Discharge Mapping Tool

Step 1.

Enter the location of the site/facility.

  1. Enter the address or latitude/longitude of your site/facility into the "Find address or place" box.
  2. Click the <enter key> or the magnifying glass icon to zoom the map to that location.

Step 2.

Draw your site/facility or discharge point locations on the map.

  1. On the map, zoom in to your site/facility location.
  2. Click the Draw Fixed Polygon or Draw Freehand Polygon button above the map, and draw an outline of your site/facility.


Click the Draw Point button above the map, and draw your site/facility’s exact discharge point(s) (i.e., outfalls).

Step 3.

Click "Execute Query" below the map.

The mapping tool provides an output table that includes information about the surface waters to which you discharge, including:

  • Any surface waters to which you discharge that are impaired and the pollutants for which they are impaired; and
  • Any surface waters to which you discharge that have a TMDL and the pollutants for which there is a TMDL.

Note: If you selected multiple points or polygons, they all are processed when you click Execute Query.

Managing Your Map

  • To delete a point or polygon, select it and click Delete Shape.
  • To remove all points and polygons, click Clear All Points/Polygons.
  • To save the map, click Save Map for Later to create a unique link that you can bookmark or share with others that contains all the points and polygons that were entered. Upon navigating to that link, the points and polygons will populate automatically on the map.

For questions or comments about the tool, email