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CSO Wet Weather Advisory

Combined Sewer overflow (CSO) outfalls may discharge stormwater mixed with untreated sewage during or following rainfall or snowmelt and may contain bacteria that can cause illness. Avoid contact or recreation (swimming, boating, and fishing) within the waterbody during or following rainfall or snowmelt.

Combined sewer overflow (CSO) sign advising people to avoid contact with the waterbody during and following wet weather events.
Example of a sign posted at a combined sewer overflow
(CSO) outfall. The sign advises people to avoid contact
with the water during and following wet weather events.
Photo: NYC Department of Environmental Protection.

Facilities with permitted CSO discharges are required by their State Pollutant Discharge Elimination System (SPDES) permit to post signs at all CSO outfalls to alert the public that the water may be contaminated with untreated sewage after a rainfall event. CSO discharges must also be reported to DEC, the Department of Health, the public and adjoining municipalities in accordance with the Sewage Pollution Right to Know law.

For more information about CSOs and their potential impacts, visit DEC's Combined Sewer Overflow (CSO) web page.

Find out if you live, or recreate in a CSO community.

Google Earth icon

The Combined Sewer Overflow (CSO) Outfalls Google Earth Map (requires Google Earth to be installed on your computer) has the location and overflow information for each permitted CSO in New York State.

Several municipal facilities have web pages dedicated to their CSO programs with more detailed information: New York City Department of Environmental Protection, Buffalo Sewer Authority, and Onondaga County Department of Water Environment Protection. Links to their CSO program web pages are in the right-hand column under (Links Leave DEC's website).

CSO Outfall Map and Overflow Information

The information displayed for each CSO outfall location contains the following:

  • Name of the municipal wastewater treatment facility and/or collection.
  • Name of the municipality that owns the wastewater treatment facility and/or collection system.
  • SPDES permit identification number.
  • The outfall number listed in the SPDES permit.
  • Waterbody name where the CSO outfall discharges.
  • Method the municipality uses to detect overflows at the outfall.
    • Observation - staff physically checks to see if the CSO has discharged
    • Model - predictive mathematical calculations that are based on watershed and rainfall information
    • Monitoring - equipment installed at the outfall that collects real-time water flow information that the municipality can analyze
  • Time frame of the overflow information
  • Number of overflow events - list the municipalities website if available