During storm events, wet weather flow from the City of Chicago's combined sewer system is diverted into the Metropolitan Water Reclamation District of Greater Chicago (MWRDGC)'s Tunnel and Reservoir Plan (TARP) system. When the capacity of TARP is reached, combined sewage may discharge into local waterways via combined sewer overflows (CSO) to alleviate the burden on the sewer system.

Pollution Prevention Plan
Chicago believes in the importance of safeguarding water quality, protecting the environment, and preserving the Chicago River to create a cleaner and more sustainable urban environment. Chicago's Pollution Prevention Plan aims to reduce pollutants from entering the sewer system ensuring compliance with NPDES Permit No. IL0045012 for environmental regulations to protect water quality in local waterways. Download the full plan here: Pollution Prevention Plan.

For notification of CSO and floodwater discharge events, please go to MWRDGC's website at http://geohub.mwrd.org/pages/cso.

Members of the public can sign up to receive e-mail and/or text notifications of CSO and floodwater discharge events by accessing the MWRDGC's website at http://apps.mwrd.org/CSORegistration/Register.aspx.

If a discharge from a CSO during dry weather is observed, please call 311.