A controversial plan to update Line 5 just suffered a major loss at the Michigan Supreme Court

The Michigan Supreme Court has thrown out a key permit for a project to replace part of the Line 5 oil pipeline, which runs under the Straits of Mackinac between Lake Michigan and Lake Huron. Enbridge Energy wanted to replace an aging section of the 73-year-old pipeline with a new one encased in a tunnel under the lakebed. The court ruled 6-1 that the Michigan Public Service Commission, which had approved the permit in 2023, failed to look at the full range of environmental harm and didn't properly weigh the public's right to use the Great Lakes, a protection known as the public trust doctrine. The case now goes back to the commission for a more thorough review, adding more delay to a project that's already been tied up for years.

The ruling matters beyond this one pipeline segment. The court said regulators must consider how the tunnel project would affect the entire 645-mile pipeline, not just the new tunnel section, including whether it extends the pipeline's life and what that means for spill risk and the environment. Opponents, including tribal nations and environmental groups, say this opens the door to a broader conversation about shutting down Line 5 entirely, rather than just approving the replacement segment. Enbridge says it's reviewing the decision and remains committed to operating the pipeline safely. This case is separate from other legal fights over whether Line 5 can keep operating in the straits at all, which are still working through Michigan courts.