The 645-mile pipeline crosses through Michigan on its route between Superior, Wis., and Sarnia, Ontario, Canada. Enbridge applied to the state to rebuild the section crossing the Straits of Mackinac, proposing to replace a pair of 20-in.-dia pipes resting on the lake bottom with a single 30-in.-dia pipe inside a concrete-lined tunnel below the lakebed.

The commission conditionally approved the application in December 2023, and last year Enbridge selected a joint venture of Barnard Construction Co. and Civil and Building North America to lead construction. 

But several Native American tribes and environmental advocacy groups appealed its decision over potential environmental risk concerns. They argued that state officials erred by limiting their review to the need for the replacement segment, rather than the full pipeline, and that officials inadequately analyzed greenhouse gas emissions related to the plan. 

Map courtesy U.S. Army Corps of Engineers, Detroit District

“We are disappointed, but not surprised by this decision,” said Whitney Gravelle, president of the Bay Mills Indian Community, one of the tribes that appealed the state decision, in a statement. “We will continue to press forward in this fight.”

An Enbridge representative said in a statement that the tunnel “makes what has always been a safe pipeline even safer” and ensures reliable access to energy. 

“As we proceed with this modernization project, we remain committed to operating Line 5 responsibly with enhanced safety measures in the Straits that protect Michigan’s natural resources and infrastructure,” the company said.

The pipeline has an average capacity of 540,000 barrels per day of light crude oil, synthetic crude and natural gas liquids, according to Enbridge. 

Even with the state permit affirmed, another state court is set to rule soon in a suit by state Attorney General Dana Nessel to shut down the line immediately as unsafe and in danger of rupture because of its age. Arguments by Nessel and defendant Enbridge were heard in January. 

Enbridge also still needs environmental impact approval from the U.S. Army Corps of Engineers before it can proceed with work. Agency officials have estimated they will complete that review and reach a permit decision next year, although the project is on a just posted list of project permit applications that President Donald Trump has directed to be expedited under an executive order. 

The Corps declined to estimate the timeframe for the permit or detail the scope of review an expedited project would get.