The Michigan Supreme Court has instructed state regulators to reexamine a critical permit for a planned tunnel that would carry an oil pipeline beneath the Great Lakes, intensifying uncertainty over the future of the 73-year-old infrastructure. The pipeline, owned by Canadian energy transportation company Enbridge Inc., transports petroleum between Superior, Wisconsin, and Sarnia, Ontario.
The contested segment, known as Line 5, spans approximately six kilometers along the bottom of the Straits of Mackinac, where Lakes Huron and Michigan converge. Enbridge’s proposal involves encasing this portion of the pipeline within a tunnel beneath the straits, a move the company says would significantly reduce the risk of an oil spill. However, environmental activists and Michigan Governor Gretchen Whitmer argue that shutting down or rerouting the pipeline away from the straits completely is imperative to prevent a potential environmental catastrophe in the Great Lakes region.
In 2023, the Michigan Public Service Commission granted Enbridge a permit to construct the tunnel, but the decision faced legal challenges from four Michigan tribal nations and several environmental organizations. On Friday, the state’s highest court ruled 6-1 that regulators did not adequately assess whether the tunnel project would effectively extend the pipeline’s operational life, potentially causing further environmental harm. The court also found the commission inconsistent in evaluating alternatives to the pipeline, including transporting oil by truck or train, and insufficient in examining the tunnel’s effects on fishing, boating, and other public trust uses of the Great Lakes.
Opponents have emphasized that this type of tunnel construction is unprecedented and expressed concern about the impact on the Straits of Mackinac, which hold cultural and spiritual significance for the Indigenous Anishinaabe tribes. “Whether Line 5 is suspended in the water or encased in a tunnel, it is simply a terrible idea to pump more than half a million barrels of oil every day through the middle of the Great Lakes,” said attorney David Gover of the Native American Rights Fund.
Enbridge has expressed disappointment in the ruling, highlighting that the project has been under evaluation for nearly a decade. Company spokesperson Ryan Duffy stated that the tunnel would enhance environmental protections for the Great Lakes region while maintaining critical energy reliability. The proposal emerged following an incident in which a ship’s anchor damaged part of the pipeline, prompting concerns over its safety.
Meanwhile, Governor Whitmer and other state officials have pursued separate legal efforts since 2020 to shut down the pipeline segment running under the straits altogether. The latest court decision adds complexity to the ongoing dispute over the pipeline’s future amid balancing environmental risks and regional energy needs. Enbridge continues to review its legal options in response to the ruling.