What is an SSO?
A sanitary sewer overflow (SSO) occurs when raw or partially treated sewage escapes from the sewer collection system before it reaches a wastewater treatment plant. Unlike combined sewer overflows (CSOs), which occur in older cities that mix storm water and sewage in the same pipes, SSOs happen in dedicated sanitary sewer systems that are supposed to carry only household and industrial wastewater.
SSOs can spill out of manholes onto streets, back up into basements, discharge into storm drains, or flow directly into rivers, lakes, and coastal waters. They carry pathogens including E. coli, norovirus, hepatitis A, and Cryptosporidium — posing direct health risks to anyone who comes into contact with the affected water or soil.
The causes range from aging and cracked pipes that allow groundwater to infiltrate the system, to grease and debris blockages, to tree roots puncturing pipe walls, to pump station failures, to extreme rainfall events that overwhelm pipe capacity. Some utilities experience hundreds of SSOs per year.
The EPA estimates more than 75,000 SSOs occur annually in the United States.
America's sewer collection system spans nearly a million miles, much of it over 50 years old.
The EPA's Clean Watersheds Needs Survey estimates a $271 billion 20-year funding gap for wastewater infrastructure.
Why this map exists
The EPA collects SSO reports from permitted utilities across the country through its NPDES (National Pollutant Discharge Elimination System) program. Utilities that experience SSOs are required to report them to their state permitting authority, and this data flows into the EPA's ECHO (Enforcement and Compliance History Online) system.
But ECHO is designed for regulators, not the public. Its interface is complex, the data is buried in bulk downloads, and there's no map view that lets an ordinary resident check whether their local utility has been spilling sewage into their river.
The UK's Surfers Against Sewage sewage map showed that public transparency around sewage discharges drives accountability. After it launched, media coverage and public pressure contributed to new legal requirements and utility investments. This map aims to do the same for the United States.
All data on this map comes directly from EPA ECHO — a federal government source. We parse and display it; we do not modify it. If an SSO event does not appear here, it either was not reported or has not yet been published in the ECHO database.
How to read the map
Volume colors
Clusters
When multiple events occur in the same area, they are grouped into a cluster circle showing the count. Click a cluster to zoom in and see individual events.
Filters
Use the sidebar to filter by state, date range, cause type, and volume. The "near me" search lets you enter a ZIP code or city to center the map on your area and see nearby events in the list.
Data source and limitations
Source:All SSO event data is sourced from the EPA's ECHO (Enforcement and Compliance History Online) database, specifically the SSO event bulk download. The data reflects reports submitted by NPDES-permitted facilities to their state environmental agencies and then to the EPA.
Completeness: Not all SSOs are reported. States vary widely in their reporting requirements, inspection capacity, and compliance rates. The actual number of SSOs is likely substantially higher than what appears in this database. Zero events in an area does not mean zero overflows.
Volume accuracy: Reported volumes are estimates made by the utility at the time of the event. These estimates may be imprecise, particularly for large spills where measurement is difficult.
Update frequency: This map refreshes from EPA ECHO daily. ECHO itself may lag actual reporting by days to weeks depending on state agency processing times.
Geographic data: Events without valid coordinates are loaded into the database but cannot be shown on the map. They still appear in the event list when filtered by state.
What you can do
- →Contact your utility: If you see frequent SSOs from your local utility, contact them directly or attend their public rate-setting and capital improvement meetings.
- →File a public records request:State environmental agencies keep SSO complaint and inspection records. Request them under your state's public records law.
- →Support infrastructure funding: Many SSOs stem from pipes that are 50–100 years old. Federal infrastructure programs like the Clean Water State Revolving Fund provide low-interest loans for upgrades — but utilities must apply and communities must prioritize it.
- →Report what you see: If you witness a sewage spill, contact your local water utility, state environmental agency, or EPA regional office.