With the U.S. Army Corps of Engineers completing its federal environmental review of the proposed Line 5 tunnel beneath the Straits of Mackinac, the decision now largely shifts to Michigan regulators. State permits — and ongoing court battles — will determine whether the controversial project moves forward.
For Michigan businesses, energy customers and environmental advocates, the stakes could not be higher.
What Just Happened
The Army Corps released its final Environmental Impact Statement (EIS) evaluating Enbridge’s proposal to construct a roughly four-mile tunnel deep beneath the Straits of Mackinac. The tunnel would house a replacement segment of Line 5, removing the existing dual pipelines that currently lie exposed on the lakebed.
The Corps’ review focuses on environmental impacts tied to tunnel construction, including potential effects on wetlands, water quality, wildlife habitat and cultural resources. A final federal permitting decision is expected soon.
But federal sign-off alone does not greenlight the project.
Michigan’s Department of Environment, Great Lakes, and Energy (EGLE) must still issue key state permits, including water discharge and wetlands approvals. Additional legal challenges surrounding easements and state authority also remain unresolved.
In short: The federal review may be finished. The political and legal battle in Michigan is not.
What Is Line 5?
Enbridge operates Line 5, a 645-mile pipeline built in 1953 that runs from Superior, Wisconsin, through Michigan and into Ontario, Canada.
The most controversial segment crosses the Straits of Mackinac, where two 20-inch pipelines rest on the lakebed connecting Lakes Michigan and Huron.
Line 5 transports crude oil and natural gas liquids (NGLs) used to produce propane and other fuels. The pipeline supplies refineries in the Midwest and Ontario and provides a significant portion of propane used in Michigan’s Upper Peninsula.
That geography — oil flowing through one of the most environmentally sensitive freshwater systems on Earth — is at the heart of the controversy.
The Case for Keeping Line 5 Open
Supporters of the pipeline argue the debate must begin with energy reliability and economics.
1. Energy Security
Line 5 helps supply propane used for home heating, particularly in northern Michigan and the Upper Peninsula. It also feeds refineries that produce gasoline, diesel and jet fuel.
Business groups warn that abruptly shutting down Line 5 could disrupt supply chains and increase fuel prices across the Midwest. Some studies suggest alternatives — including rail or truck transport — could introduce higher costs and potentially higher accident risks.
2. Economic Impact
The tunnel project itself represents a multi-billion-dollar infrastructure investment. Supporters argue it would generate construction jobs and long-term operational employment while modernizing aging infrastructure.
Michigan’s manufacturing sector — including automotive and logistics operations — remains heavily dependent on reliable fuel supplies. Energy volatility is not something corporate planners welcome.
3. Tunnel as a Safety Upgrade
Enbridge maintains that burying the pipeline inside a concrete-lined tunnel approximately 100 feet below the lakebed dramatically reduces spill risk compared to the current exposed pipes.
From this perspective, the tunnel is not an expansion — it is a safety modernization.
The Case Against Line 5
Opponents argue that even with a tunnel, the risks outweigh the benefits.
1. Spill Risk in the Great Lakes
The Straits of Mackinac feature powerful currents that can move in multiple directions. Environmental groups warn that a rupture could spread oil rapidly across both Lakes Michigan and Huron.
The Great Lakes contain roughly 20% of the world’s surface freshwater. Tourism, fisheries and drinking water systems could face catastrophic damage in a worst-case spill scenario.
Anchor strikes in recent years heightened public concern, even though they did not result in major spills.
2. Climate Policy Conflicts
Critics argue that approving a new tunnel would extend fossil fuel infrastructure for decades at a time when Michigan and the U.S. are pursuing carbon reduction goals.
From their perspective, the project locks in long-term oil transport rather than accelerating transition to renewables.
3. Tribal Sovereignty and Treaty Rights
Several Native American tribes oppose the project, citing treaty rights, cultural concerns and environmental protection responsibilities tied to the Great Lakes.
Legal challenges have centered not only on environmental impacts but also on questions of state authority and federal jurisdiction.
The Legal Chessboard
The Line 5 dispute has already traveled through multiple courts.
Michigan officials have attempted to revoke the pipeline’s easement under the Straits, arguing it violates public trust protections. Enbridge has countered that pipeline regulation falls under federal jurisdiction.
A federal judge previously ruled that Michigan could not unilaterally shut down the pipeline, pushing the dispute into federal court.
Separate litigation continues over state permits and easement validity. Appeals could ultimately determine whether the tunnel proceeds — or whether the existing pipeline must eventually cease operations.
Why This Matters to Michigan Business
For MITechNews readers, the story is bigger than environmental politics.
Energy reliability affects:
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Manufacturing production schedules
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Transportation costs
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Data center operations
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Agricultural inputs
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Residential heating affordability
If Line 5 were shut down without replacement infrastructure, the Midwest energy market would have to rebalance quickly. Rail shipments and alternative pipelines could fill gaps, but likely at higher cost.
Conversely, a major spill in the Straits could devastate tourism, fisheries and shoreline property values — industries that also underpin Michigan’s economy.
In other words: The risk calculus runs both ways.
What Happens Next?
The Army Corps’ review is complete, but Michigan regulators now carry the weight of decision.
EGLE must determine whether the tunnel meets state environmental standards. Courts will continue weighing legal challenges. Political pressure from both sides will intensify.
The debate over Line 5 has stretched across multiple governors, courtrooms and election cycles. It is unlikely to end quietly.
For Michigan, this is a defining infrastructure question:
Is the tunnel a pragmatic safety upgrade that protects energy stability?
Or is it an unnecessary extension of fossil fuel risk in the heart of the Great Lakes?
State regulators will soon move from review to decision.
And whichever way they rule, the economic, environmental and political ripple effects will extend far beyond the Straits of Mackinac.
