Where Combined Sewer Overflow Outfalls Are Located
There are approximately 700 communities in the United States that have combined sewer systems and experience combined sewer overflow (CSO) discharges. These communities are mostly located in the northeast and around the Great Lakes. The map below shows CSO outfall locations throughout the United States.
In addition to the map below, find details about CSOs in the Great Lakes Basin.
Click on the map to access more detailed information about each active CSO outfall, such as National Pollutant Discharge Elimination System (NPDES) permittee and receiving waterbody, as well as detailed information on compliance and enforcement from Enforcement and Compliance History Online (ECHO).
Notes on the data:
The data supporting this map are from the National Combined Sewer Overflow Inventory. The National Combined Sewer Overflow Inventory was first published to ECHO in May 2023 to reflect the most current inventory of CSO outfalls across the United States. These data are updated weekly in the Integrated Compliance Information System NPDES (ICIS-NPDES). ICIS-NPDES is an information management system maintained by EPA to track permit compliance and enforcement status of facilities regulated by the NPDES permitting program under the Clean Water Act. ICIS-NPDES is designed to support the NPDES program at the state, regional, and national levels.
States are actively working to update and correct data in ICIS-NPDES. EPA estimates that approximately 90 percent of CSO outfalls have been verified by the state permitting authority in the National Combined Sewer Overflow Inventory (as of September 2023). This feature service contains data from active CSO outfalls only.
A compressed zip file containing comma-delimited text files of both active and closed CSO outfalls is available for download at ECHO Data Downloads.