The US Army Corps of Engineers has granted a federal permit for the controversial Line 5 tunnel project beneath the Straits of Mackinac in Michigan, clearing a major regulatory hurdle for Enbridge Energy.
The project would move a section of the Line 5 petroleum pipeline from open water into a concrete tunnel constructed beneath the lakebed.
In its decision, the Army Corps concluded that the project is “not contrary to the public interest” and would not violate tribal treaty rights.
However, the agency also acknowledged several environmental and cultural impacts, including effects on endangered species, archaeological sites and surrounding habitats.
Environmental and cultural concerns remain
According to the Army Corps, construction and operation of the project could adversely affect Houghton’s goldenrod and dwarf lake iris, two threatened plant species.
Mitigation measures are expected to prevent a broader decline in their populations or distribution, the agency said.
The project would also have permanent impacts on historic properties and archaeological sites. The area is considered culturally and spiritually significant by Anishinaabe tribal nations, which have strongly opposed the tunnel.
Opponents argue that damage to sacred and archaeological sites cannot simply be mitigated.
Enbridge welcomes federal approval
Enbridge welcomed the federal decision, describing the permit as an important step for the project and reiterating its position that Line 5 can continue to operate safely.
The company said it would maintain enhanced safety measures around the Straits while continuing efforts to protect Michigan’s natural and cultural resources.
The Trump administration also presented the approval as part of its broader strategy to strengthen US energy infrastructure and reduce regulatory barriers for major energy projects.
Construction still faces major obstacles
Despite the federal permit, construction is not expected to begin immediately.
The project remains subject to ongoing legal and regulatory challenges. The Michigan Supreme Court recently ordered state energy regulators to reconsider a separate permit, while the project continues to face litigation in both state and federal courts.
Opponents have also indicated that further legal challenges are likely.
Enbridge is separately seeking approval to discharge treated wastewater into Lake Michigan during construction. Michigan’s Department of Environment, Great Lakes and Energy is expected to make a decision on that permit by September 30.
Line 5 remains at the centre of a wider legal dispute
The tunnel proposal is closely linked to the broader dispute over the existing Line 5 pipeline.
Michigan Governor Gretchen Whitmer ordered the pipeline to shut down in 2020 over concerns about a potential oil spill in the Straits of Mackinac. Enbridge challenged the order, and the legal battle remains unresolved.
The latest federal approval therefore moves the tunnel project forward, but major legal, environmental and regulatory questions remain before construction can proceed.
