An employee error led to the wastewater leak at the South Shore Water Reclamation Facility in Oak Creek earlier this month. The treatment facility overflow resulted in 10,000 gallons of untreated wastewater being released into Lake Michigan.
At 5:30 p.m. on Sept. 18, 2025, an employee with Veolia Water Milwaukee, a contractor of the Milwaukee Metropolitan Sewerage District, observed wastewater overtopping the emergency overflow structure at the South Shore facility, according to a summary report submitted by the sewerage district to the Wisconsin Department of Natural Resources on Sept. 23. The sewerage district is required to submit a report to the DNR within five days of an overflow.
The treatment facility overflow occurred during staff shift change, “which likely contributed to the error,” the report says.
The overflow lasted approximately 30 minutes. While the sewerage district’s original estimate suggested about 20,000 gallons of wastewater overflowed, half of that was recovered and treated.
There is a potential for human exposure through recreational use of the waterway, the report says.
According to the report, too much water came though a gate when it shouldn’t have, and untreated wastewater overtopped an emergency barrier.
Corrective actions were taken right away to stop the overflow, the report says. Employees adjusted the gates and valves, wastewater was pumped out and treated, and the system was cleaned to remove any remaining sewage. These actions are expected to be completed by Sept. 30.
“It’s not something that we are taking lightly,” Paul Keppler, vice president and general manager at Veolia, told the Milwaukee Journal Sentinel.
Keppler said the employee that allowed the overflow to occur faced disciplinary action, and Veolia is in the process of implementing a more robust turnover process so this does not happen in the future.
This is second release caused by human error this year
This is the second untreated wastewater spill caused by Veolia this year.
In March, nearly 10,000 gallons of wastewater was mistakenly leaked into Lincoln Creek and the Milwaukee River when workers from Veolia released the wastewater into a storm sewer rather than a sanitary sewer.
After the March spill, Veolia Water Milwaukee told the Journal Sentinel that there were numerous pipelines and manholes in close proximity at the location, and the workers picked the wrong one.
Veolia also said in March that the situation was unusual, and adjustments were made to protocols to ensure the mistake would not happen again. Veolia also scheduled refresher training for its field crews on proper discharge procedures.
There was also an incident in April when about 1,000 gallons of wastewater leaked into Lake Michigan from the sewerage district’s South Shore facility, but that was due to a broken pipe.
More: With days as a target long past, MMSD’s Kevin Shafer focuses on a cleaner, greener Milwaukee
More: Naturalized streams, rivers may have prevented worse flooding. MMSD spent $580 million.
Caitlin Looby covers the Great Lakes and the environment for the Milwaukee Journal Sentinel. Reach her at clooby@gannett.com, and follow her on X @caitlooby.
Caitlin’s work is supported by the Brico Fund, Fund for Lake Michigan, Barbara K. Frank, and individual contributions. Grants and donations help make this reporting possible. The Journal Sentinel maintains full editorial control.
To learn more about our community-funded journalism initiatives, or to make a tax-deductible donation, visit https://givebutter.com/milwaukee-journal-sentinel. Checks can be addressed to Local Media Foundation with “JS Environment” in the memo, then mailed to: Local Media Foundation, P.O. Box 85015, Chicago, IL 60689.
This article originally appeared on Milwaukee Journal Sentinel: Human error caused wastewater overflow into Lake Michigan