Michigan's Supreme Court sent Enbridge's Great Lakes Tunnel permit back for reconsideration.
Why it matters: The ruling keeps scrutiny on Enbridge's effort to build a tunnel for Line 5 under the Straits of Mackinac. It also shows Michigan regulators and courts still hold major sway over the project's path.
- The Michigan Supreme Court ruled 6-1 on July 31, 2026, to send the permit back for reconsideration.
- The permit was approved by the Michigan Public Service Commission in 2023 for the Great Lakes Tunnel project.
- The tunnel would house a replacement segment of Line 5 beneath the Straits of Mackinac.
- Michigan's Department of Natural Resources issued a separate Line 5 permit on July 15, 2026, while the U.S. Army Corps of Engineers is still reviewing the tunnel.
The Michigan Supreme Court's 6-1 ruling sent Enbridge's tunnel permit back to state regulators for reconsideration, according to AP. The permit had been approved by the Michigan Public Service Commission in 2023 for a tunnel that would carry a replacement segment of Line 5 beneath the Straits of Mackinac.
AP reported that the court said regulators did not adequately assess whether the tunnel would extend the life of Line 5, whether alternatives were evaluated consistently and how the project would affect fishing, boating and other public trust interests. The pipeline carries petroleum from Superior, Wisconsin, to Sarnia, Ontario, with a roughly 4-mile segment running beneath the straits.
The Detroit Free Press reported that the decision sends the permit back to regulators rather than ending the project. Enbridge has said the Great Lakes Tunnel would cost $500 million, and the company has described the project as intended to improve environmental protection while maintaining energy reliability for the region, AP reported.
Michigan's Department of Natural Resources issued a separate permit on July 15, 2026, and the U.S. Army Corps of Engineers is still reviewing the tunnel proposal, according to the briefings from AP and the Free Press. Those reviews remain part of the broader regulatory process around Line 5.
By the numbers
- 6-1 - Michigan Supreme Court vote to send the permit back.
- $500 million - Enbridge's stated cost for the Great Lakes Tunnel.
- July 15, 2026 - Date the Michigan Department of Natural Resources issued a separate Line 5 permit.
Yes, but: The ruling sends the permit back for reconsideration, but it does not decide whether the tunnel will ultimately be approved.
What's next: State regulators must reconsider the permit. The U.S. Army Corps of Engineers is still reviewing the tunnel proposal.