CSO Wet Weather Advisory
Advisory for CSO outfalls during and following rainfall and snowmelt events
Facilities with permitted CSO discharges are required by law to post signs at all CSO outfalls to alert the public that the water may be contaminated with untreated sewage after a rainfall event.
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.
CSO outfalls may discharge rainwater mixed with untreated sewage during or following rainfall or snowmelt events and may contain bacteria that can cause illness.
Avoid contact or recreation (swimming, boating, and fishing) within the waterbody during or following a rainfall or snowmelt event.
To find CSO outfall locations, visit DEC's Google Maps web page and open the "Combined Sewer Overflow (CSO) Outfalls" map located in the "Environmental Maps" table; maps are listed in alphabetical order. The map provides location and general facility information, receiving waterbody, BMPs required in the facility's permit, and the status of the permittee's LTCP.
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 Leaving DEC's website".
Potential Impacts of CSOs discharges
Discharges from CSO outfalls may contain mixtures of domestic sewage, storm water runoff, and sometimes, industrial wastewater, including: high levels of suspended solids, toxic chemicals, floatable material and other pollutants.
The polluted CSO outfall discharge may:
- cause a waterbody to exceed NYS water quality standards,
- impact human and aquatic health,
- lead to bathing beach closures due to bacterial contamination
- aesthetic impacts due to floating debris or slicks,
- close shellfishing beds,
- promote the growth of algae, and
- reduce oxygen levels in the water.
