(The Center Square) – Environmental groups and Native American tribal nations argued before the Michigan Supreme Court in their ongoing challenge against the Great Lakes Tunnel Project, which is slowly making its way out of regulatory and legal limbo.
Attorneys representing the coalition asked the court to overturn a lower court’s decision to uphold the Michigan Public Service Commission’s approval of the tunnel project. They argued the court applied the wrong legal standard and failed to properly evaluate environmental risks under the Michigan Environmental Protection Act.
“The tunnel project is a climate and freshwater disaster,” said Denise Keele, executive director of the Michigan Climate Action Network. “While the court weighs this challenge, we call on Governor Whitmer and our state regulators to listen to the tens of thousands of Michiganders who value our Great Lakes and deny any new permits for the tunnel project.”
Enbridge told The Center Square that it believes the permit should be upheld.
“We have full confidence in the Michigan Public Service Commission’s diligent and comprehensive review of the Line 5 tunnel project,” it said in a statment on Thursday. “The MPSC’s rigorous evaluation led to the approval of locating the pipeline into the safety of a deep underground tunnel, an approach designed to protect the Great Lakes while maintaining energy reliability.”
The legal challenge was brought by the Environmental Law & Policy Center and the Michigan Climate Action Network, alongside several tribal governments. The tribal nations are represented by the Earthjustice and the Native American Rights Fund.
On Wednesday, the coalition urged the court to send the case back to the commission for further review, arguing the agency did not conduct the rigorous environmental analysis required under the law before approving the permit in 2023.
In a separate legal challenge, Flow Water Advocates argued on Wednesday the commission should have rejected the project under the public trust doctrine, which requires the state to protect public waters for residents.
“The Straits of Mackinac belong to all of us, and the State has a duty to protect them,” said Whitney Gravelle, president of the Bay Mills Indian Community. “Tribal Nations have treaty-protected rights to fish, hunt, and gather in these waters, rights that cannot exist if the resources they depend on are put at risk.”
The proposed changes to Line 5 would move a section of the pipeline into a tunnel under the Straits of Mackinac, which is the four-mile-wide waterway connecting Lake Michigan and Lake Huron and dividing Michigan’s Upper and Lower peninsulas. The pipeline currently lies on the bottom of the Straits.
The transmission line is owned by Canadian company Enbridge and goes 645 miles from Superior, Wisconsin, through the Straits of Mackinac in Michigan to Sarnia, Ontario. The 72-year-old pipeline currently moves more than 500,000 barrels of oil and natural gas liquids daily.
The Michigan Public Service Commission approved the tunnel permit in 2023, a decision upheld by the Michigan Court of Appeals in 2025. The environmental groups and tribal nations then appealed to the Michigan Supreme Court. If the court sides with the challengers, the permit could be vacated and the case sent back to the commission for additional review.
Along with the state permit, federal regulators are also considering whether to grant final approval. In February, the U.S. Army Corps of Engineers recently released its final Environmental Impact Statement examining the potential environmental effects of the tunnel project, as previously reported by The Center Square.
That report evaluated impacts ranging from geology and water resources to wildlife, transportation and air quality, finding some short-term construction impacts but potential long-term benefits once the tunnel is completed. Following a 30-day period of public comment, that statement will help inform the agency’s Record of Decision—which should be released soon.
Supporters of the project argue the tunnel would make the pipeline safer and Michigan’s economy stronger.
“Locating Line 5 in a tunnel deep below the lakebed at the Straits will make an already safe pipeline even safer, enhancing energy reliability, protecting access to the fuels people depend on, and supporting jobs and the regional economy. The project continues to have the support of a majority of Michiganders,” Enbridge told The Center Square. “As we advance this important modernization effort, we remain committed to operating Line 5 responsibly, with enhanced safety measures in the Straits that safeguard Michigan’s natural resources.”
Opponents, including many Democrats, have argued the project threatens the Great Lakes and have called for Line 5 to be shut down entirely. There is only one Republican on the seven-member Michigan Supreme Court.
The eight-year project, which has yet to break ground, is currently being expedited as a result of President Donald Trump’s day one executive order declaring a national energy emergency.
This is just one of the lawsuits currently filed against the Great Lakes Tunnel Project. There is also a case in federal court which the U.S. Supreme Court is currently reviewing.
