Posted on November 4, 2026
In an effort to clean up more than a century of pollution in Milwaukee’s waterways, a 42-acre “bathtub” has opened along Lake Michigan to hold tons of toxic sediment.
The $123 million facility, known as the Dredged Material Management Facility, or DMMF, was completed in October. It can hold 1.9 million cubic yards of contaminated sediment dredged up from rivers in southeast Wisconsin. That’s equivalent to approximately 13 football fields filled to a depth of 50 feet.
More than 100 years before modern pollution control laws, companies dumped sediments into the waterways, some of it containing cancer-causing toxins like PCBs (polychlorinated biphenyls), PAHs (polycyclic aromatic hydrocarbons) and heavy metals.
“That contaminated sediment is causing a lot of impacts to the very bottom of the food chain, the insects at the bottom of the river. It’s getting into the fish, it’s getting into people eating the fish,” Cheryl Nenn, the riverkeeper for Milwaukee Riverkeeper nonprofit, told WPR’s “Wisconsin Today.”
The toxic sediment to fill the tub-like facility will come from Milwaukee, Menomonee and Kinnickinnic Rivers. Where those three rivers meet and flow into Lake Michigan is known as the Milwaukee Estuary, which became a designated “area of concern” by the U.S. and Canada in 1987, one of 31 along the Great Lakes. That designation allowed for federal dollars to flow to the DMMF project.
Dredging boats will essentially vacuum up sediment from deep in the riverbeds that will then be tunneled to the facility. But how will officials ensure this toxic sediment is contained and won’t leak into Lake Michigan, Milwaukee’s primary drinking water source?
“That is the biggest question we get from a lot of different folks,” said Bridget Henk, the principal project manager at the Milwaukee Metropolitan Sewerage District and leader of the project.
Part of the bathtub design is a 2.5-to-3-foot-thick wall around the entire perimeter. The wall, called a soil mix cutoff wall, is an impermeable surface, according to Henk. Monitors track water levels ensuring they differ inside and outside the facility. If the water levels ever equalize, that means sediment is leaking and the monitors will alert officials.
Although there are plenty of facilities across Wisconsin and the U.S. that hold dredged material — including directly next to the new DMMF facility — what makes this one unique is the toxicity of the material. Most others hold non-contaminated material removed from waterways to maintain shipping channels.
Nenn said although preventing pollutants from entering the waterways is ideal, dredging is a tool environmentalists use to help restore waterways, and in this case, improve water quality.
“We really do think this is a generational opportunity to clean up a lot of this legacy contamination,” Nenn said. “It is really getting us closer to our ultimate goals, which are clean rivers that can be used for things like swimming and fishing and drinking.”
Over the next 20 to 30 years, the facility will fill up and the sediment will be its long-term home. Hentz said the bathtub could be capped in the future with something built on top of it. But those decisions will be for the City and Port of Milwaukee to decide, as they take over ownership.
