In a win for opponents of Enbridge Energy’s Line 5 pipeline, the Michigan Supreme Court vacated a key permit last week for a proposed project that would replace a segment of the pipeline running underneath an environmentally-sensitive area of the Great Lakes, finding that a state commission did not examine the full scope of possible harm to the environment.

Following the 6-1 decision, the justices remanded the permit back to the Michigan Public Service Commission for a more thorough review, which likely extends the timeline for a decision on a project that’s already been mired in legal and procedural hurdles for years.

Enbridge Energy received the permit in 2023 for its proposal to replace a segment of the oil and natural gas liquids pipeline — which connects lakes Michigan and Huron via the Straits of Mackinac — with a new one encased in a tunnel buried in the lakebed. Environmental groups and tribal nations appealed the decision, landing the case before the state’s highest court this year.

Writing for a nearly unanimous court in a 58-page opinion, Justice Elizabeth Welch said that the commission didn’t consider the full range of potential environmental harms, nor did it look at how the project would impact the public’s right to use the state’s natural resources, which includes the Great Lakes — protections granted under the state’s public trust doctrine.