Chicago’s Sewage Overflow Problem: How You Can Help Prevent Flooding and Pollution

As little as 0.3 inches of rain can result in untreated sewage water flowing into the region’s rivers. The practice of releasing untreated waste is a tradeoff to help prevent flooding events that have plagued Chicago for decades. Combined sewer systems (CSOs), miles of concrete infrastructure, and heavy rainfall contribute to the issue. The increase in extreme rain events is overwhelming the city’s sewer system, polluting water, and costing homeowners thousands of dollars. In response to ongoing sewage releases into surface waters, Overflow Action Days were launched to mitigate the impact.

For nearly a decade, Friends of the Chicago River has used this innovative program to educate the public on limiting water usage to reduce the strain on sewer systems during rain events. To date, 8,000 subscribers receive e-alerts in coordination with the Metropolitan Water Reclamation District (MWRD), monitoring over 300 outfalls into the Chicago River and Little Calumet River, according to Director of Communications Tim Tuohy.

The initiative follows the success of Ozone Action Alert days, an air quality alert system that helps the public understand risks to vulnerable populations. However, Overflow Action Alerts serve a dual purpose — not just warning of potential flood conditions but also reminding the public to reduce unnecessary water usage during heavy rainfall. By minimizing household water use, residents help prevent excess water from overwhelming the sewer system.

CSOs can only handle a limited volume of water at a time. When excessive water enters the 4,500 miles of sewers through any of the 146,000 manholes or 205,000 collection structures too quickly, streets and basements back up with a mixture of sewage and rainwater. Tuohy is confident that the alert system is making a difference.

“It’s our experience that when people become educated about water," he said, "they take everyday actions to help prevent sewer overflows—simple tasks like holding off on laundry and running the dishwasher make a huge difference.”

In recent years, the importance of water literacy and public outreach has become even more apparent. Record-breaking rainfall in the spring of 2020 led to Chicago’s sewers being overwhelmed for 11 consecutive days — the wettest May ever recorded, according to the National Weather Service. Flash floods created hazardous conditions, forcing the reversal of the Chicago River, sending water back into Lake Michigan. The following year, MWRD, with support from Friends of the Chicago River, designated April as Overflow Action Awareness Month.

MWRD Alerts Remind the Public to:

- Delay or reduce shower times

- Put off running the dishwasher

- Wait to do laundry

- Replace old, leaky faucets, toilets, and showerheads with water-efficient models

These alerts help residents organize their daily water usage, reducing strain on the sewer system. Additionally, CSOs and Chicago River reversals to Lake Michigan can now be tracked using real-time data.

The implementation of the Tunnel and Reservoir Plan (TARP) has reduced the frequency of river reversals from the Chicago Area Waterway System (CAWS) to Lake Michigan. There are two types of reversals:

1. Gate reversals – More frequent, involving a smaller volume of water released through adjacent gates to the lock.

2. Lock reversals – Less common, occurring when locks are opened to allow a larger volume of water to flow back into Lake Michigan, typically during severe storm events.

The use of GIS mapping tools, such as Esri GIS software, has enhanced public awareness by tracking CSO activity in real time. With real-time CSO information, residents can make informed decisions about water-related activities and better understand water quality trends. By increasing transparency, stakeholders can collaborate to improve the quality and sustainability of local water resources.

Anyone can sign up for Overflow Action Alerts — it’s free and easy at chicagoriver.org.

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