Maryland Reported Sewer Overflow Database

The Maryland Department of the Environment (MDE) maintains publicly accessible data on bypasses, combined sewer overflows (CSOs) and sanitary sewer overflows (SSOs) reported to MDE from January 2005 through the most recent update on Maryland’s Open Data Portal. Although MDE requires that all public sewer system owners or operators report overflows to us, there may be incidents that were not reported. Note that overflow amounts provided by the person reporting the overflow may be estimated using best professional judgment or they may be actual readings from flow measurement devices when available.

Information on overflows that occurred from January 1, 2005 through January 31, 2023 is available at

Information about overflows that have been reported since February 1, 2023 is available at​ and this dataset is currently updated monthly.

If you have any questions about this database, please contact Andrew Gosden, Program Manager at 410-537-3510.


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