MACKINAC—A long-awaited federal analysis has landed with weight, detailing serious environmental concerns linked to Enbridge Energy’s proposed tunnel beneath the Straits of Mackinac. The plan: replace the aging twin pipelines of Line 5 with a 3.6-mile underground corridor carved through bedrock, carrying 20 million gallons of oil and gas liquids per day.
The US Army Corps of Engineers’ draft environmental impact statement, released Friday, acknowledges what many Anishinaabe Nations, scientists, and environmental advocates have long said: this is no simple upgrade.
Wetlands, wildlife and water at risk
The report outlines direct, detrimental effects tied to the project—particularly during its six-year construction period. These include: permanent loss of wetlands and vegetation; disruption of groundwater systems; harm to bat habitats and aquatic wildlife from noise and vibration; obstructed recreational access due to traffic, light pollution, and crane activity; and reduced visibility of night skies at Headlands International Dark Sky Park.
While some of these impacts may subside once construction is complete, others—like habitat destruction—may leave a lasting mark. And then there’s the risk of drilling fluids escaping into surrounding waters, which the Corps identifies as a significant concern.
An old pipeline, a new tunnel and a shifting timeline
The tunnel proposal was first introduced in 2018 with an estimated cost of $500 million. Initially projected for a 2026 permitting decision, the project was fast-tracked in 2020 after a Trump-era executive order called on agencies to prioritize energy infrastructure.
Now, the Corps anticipates a final decision by late 2025, with a separate approval still required from Michigan’s Department of Environment, Great Lakes and Energy (EGLE). That approval, however, remains uncertain.
Meanwhile, Michigan Attorney General Dana Nessel and Governor Gretchen Whitmer continue to pursue legal strategies to remove the existing pipelines from the Straits altogether.
Tension between safety and expansion
Enbridge argues the tunnel would offer a safer, modern route—protecting Line 5 from anchor strikes and reducing the risk of a major spill into the open waters of the Great Lakes. That risk is real. But so are the ecological trade-offs.
The Corps’ report makes it clear that: while the tunnel may lower the likelihood of a catastrophic leak, it also introduces new environmental burdens during its construction. And critically, it extends the lifespan of fossil fuel infrastructure at a time when climate science calls for the opposite.
This isn’t just a question of where oil flows—it’s about whether it should continue to flow through the heart of the Great Lakes.
The Army Corps’ draft analysis is now open to public comment. Input gathered over the coming weeks will help shape the final report, expected by autumn.
