Duluth Slip Project Caps

150,000 Cubic Yards of

Contaminated Riverbed

Capping contaminated soil in the St. Louis River and harbor to Lake Superior prevents toxic pollution from spreading and harming fish, wildlife, and people.


The St. Louis River is the largest tributary to Lake Superior. It empties into the lake at the twin ports of Duluth, Minn., and Superior, Wis. The St. Louis River estuary serves as a nursery to more than 45 native fish and 230 bird species, including walleye, lake sturgeon, common tern, and piping plover. Historically, the area also provided an essential hub for shipping as well as industries like shipbuilding and steel production.

But the heavy industry that was essential for a growing nation also left a legacy of pollution and contamination. The St. Louis River is now listed as one of the Great Lakes region’s most contaminated sites – called an Area of Concern – due to toxic chemicals such as mercury, dioxin, and PCB in the river and harbor. The pollution has led to fish consumption advisories, beach closures, and the loss of fish and wildlife habitat. Since the late 1980s, local, state and federal partners have worked to clean up the river.

In the fall of 2018, thanks to $7.8 million from federal Great Lakes Restoration Initiative and $4.2 million from Minnesota bonds, three shipping slips underwent remedial construction to remediate toxic pollution in the lakebed. The project put clean sand and loose rock on portions of the lake- and river-bottom that had been contaminated. This sealed, or capped,” the contaminated sediment so that fish and other organisms would not be exposed to it.

Resource Challenges Addressed

  • Toxic pollution
  • Habitat Loss


Duluth Slip under construction. Photo credit: Minnesota Pollution Control Agency

Results and Accomplishments

Over 150,000 cubic yards of contaminated sediment was capped at these three sites protecting important organisms that live on the bottom of the riverbed, the fish that thrive in its waters, and people connected through the food chain.