Supreme Court Hands Michigan Major Win in Line 5 Fight—But Bigger Questions Loom on Spill Risk, Economic Fallout

The U.S. Supreme Court ruled unanimously that a lawsuit seeking to shut down Enbridge’s controversial Line 5 pipeline must be heard in Michigan state court, not federal court. That decision keeps the case where Michigan leaders want it—and where the odds of a shutdown are widely viewed as stronger.

At the center of the case is a 2019 lawsuit filed by Attorney General Dana Nessel to shut down the aging pipeline segment that runs beneath the Straits of Mackinac. Enbridge had attempted to move the case to federal court, arguing broader national and international implications. The Supreme Court rejected that effort, ruling the company waited far too long to make the move.

While procedural on its face, the decision reshapes the legal battlefield—and raises urgent questions about risk, cost, and energy supply that go far beyond the courtroom.

What If Line 5 Ruptures?

This is the question driving the entire fight—and the reason the stakes are so high.

The most controversial section of Line 5 sits on the lakebed beneath the Straits of Mackinac, where Lake Michigan and Lake Huron meet. It’s one of the most complex and fast-moving water systems in the Great Lakes.

A rupture here would not behave like a typical land-based oil spill.

According to multiple state and academic studies:

• Oil could spread rapidly in multiple directions due to shifting currents
• Shorelines in both the Upper and Lower Peninsulas could be impacted within hours
• Cleanup would be significantly more difficult, especially during winter ice conditions
• Contamination could reach critical ecosystems, fisheries, and tourism centers

The closest real-world comparison is the 2010 Kalamazoo River oil spill—also involving Enbridge—which ultimately cost more than $1 billion to clean up. But that spill occurred on land.

A major spill in the open waters of the Great Lakes is widely expected to be more complex—and potentially far more expensive.

Michigan has required roughly $1.8 billion in financial assurances tied to Line 5 risk, offering a rough benchmark of potential exposure. Many experts believe a worst-case scenario in the Straits could result in multi-billion-dollar economic damage, particularly when long-term environmental restoration and business losses are factored in.

How Many People Could Be Impacted?

The potential impact extends far beyond northern Michigan.

The Great Lakes provide drinking water to approximately 40 million people in the United States and Canada. In Michigan alone, roughly 10 million residents rely on Great Lakes-connected water systems.

A spill in the Straits could affect:

• Drinking water systems across multiple regions
• Commercial and tribal fisheries
• Tourism economies that generate billions annually
• Shoreline property values and local businesses

Because currents in the Straits can push contaminants into both Lake Michigan and Lake Huron, the geographic exposure is unusually broad.

In short, this is not a localized risk—it’s a regional one with cross-border implications.

What Happens If Line 5 Is Shut Down?

Line 5 currently transports about 540,000 barrels per day of crude oil and natural gas liquids. It plays a key role in supplying propane to Michigan—especially the Upper Peninsula—and feeds refineries in Ontario.

If the pipeline were shut down, the oil doesn’t simply disappear. It would have to move another way.

There is no single replacement solution.

Likely alternatives include:

Rail transport:
The most immediate fallback option, but significantly more expensive and statistically riskier than pipelines on a per-barrel basis.

Trucking:
Useful for shorter distances but not scalable to replace the full volume.

Alternative pipelines:
Some capacity exists elsewhere in North America, but not enough to fully replace Line 5 without rerouting and upgrades.

Marine shipping:
Great Lakes tanker transport is possible but faces seasonal and environmental constraints.

Refinery adjustments:
Facilities could shift supply sources or reduce output temporarily, though this may affect pricing.

The likely outcome would be a patchwork system that is more expensive, less efficient, and potentially introduces different types of risk.

Enbridge’s Plan B: The Tunnel

Enbridge’s long-term solution is not to abandon Line 5—but to rebuild it.

The company has proposed constructing a tunnel beneath the Straits of Mackinac, housing a new pipeline segment designed to reduce spill risk from external threats such as anchor strikes.

Supporters argue the tunnel offers a middle ground: maintaining energy supply while addressing environmental concerns.

Critics question whether the project is necessary—or whether shutting down the pipeline altogether is the safer option.

Economic Tradeoffs on Both Sides

This is where the debate becomes most complex.

Shutting down Line 5 could lead to:

• Higher propane costs, particularly in the Upper Peninsula
• Supply disruptions affecting refineries in Michigan and Ontario
• Short-term regional fuel price increases

However, energy markets tend to adapt over time through rerouting and alternative sourcing.

At the same time, leaving the pipeline in place carries the risk—however uncertain—of a high-impact environmental disaster with long-lasting economic consequences.

The Supreme Court ruling did not decide the fate of Line 5—but it may prove to be one of the most important turning points in the fight.

By sending the case back to Michigan state court, the justices shifted momentum toward state regulators and environmental arguments.

Now, the debate moves beyond legal technicalities to a far more fundamental question:

Is the economic and environmental risk of a potential Great Lakes oil spill worth the continued operation of one of North America’s most controversial pipelines?

That answer will shape Michigan’s energy future—and potentially the future of the Great Lakes themselves.