LANSING, July 17 — The technical reality of the Line 5 pipeline, which pushes up to 540,000 barrels of oil and natural gas liquids daily through the Straits of Mackinac, is that it sits at the intersection of energy supply and environmental risk. For the informed reader, the detail that matters is not just the volume of hydrocarbons moving under the lakebed, but what happens if that system fails. The pipeline, operated by Enbridge, supplies refineries across Michigan, Ohio, Pennsylvania, and Ontario.
Under the hood, its significance to the Upper Peninsula of Michigan is particularly stark: Line 5 provides about 65% of the region’s propane. That is not a marginal supply chain; it is the dominant one for heating and agriculture in a cold-weather state.
Any disruption would hit those communities hard, and fast.
The vulnerability at the Straits
The Mackinac Straits are widely regarded as the most vulnerable point on the Great Lakes system. The reason is hydrological: strong currents move through the narrow channel, and a spill there would not stay local. Oil could spread rapidly, carried by those currents into the broader lake system.
The Great Lakes contain 84% of North America’s surface fresh water — a resource that underpins a $7 billion fishing industry and a $16 billion tourism industry. Those figures are not abstract; they represent livelihoods and ecosystems that would take decades to recover from a major spill.
As ever with infrastructure of this scale, the debate turns on a single question: is the risk worth the reward? Enbridge has argued that a proposed tunnel, which would encase the pipeline in a concrete-lined passage drilled deep under the lakebed, would reduce the spill risk. The company frames the tunnel as an engineering solution to an engineering problem — a way to keep the oil flowing while hardening the system against anchor strikes, corrosion, or current damage.
Environmental groups take a different view. They argue the pipeline should be decommissioned entirely.
Their position is that no amount of engineering can eliminate the risk of a catastrophic spill in the Straits, and that the only safe pipeline is one that is not there. The technical reality on both sides is that the Straits are a choke point — geographically, hydrologically, and politically.
The economic calculus
The numbers attached to the Great Lakes economy are not small. A $7 billion fishing industry and a $16 billion tourism industry mean that the lakes are not just a scenic backdrop; they are an economic engine. A spill that contaminated significant portions of the lakes would ripple through those industries in ways that are hard to model but easy to imagine.
Cleanup in the Straits would be complicated by the same currents that make the location so risky in the first place — oil would not sit still, and containment booms would struggle against the flow. For the Upper Peninsula, the propane dependency is the detail that gives the debate its local edge.
When 65% of a region’s propane comes through a single pipeline, decommissioning is not a simple decision. It would require alternative supply routes, storage capacity, and probably higher prices in the short term. The question is whether those costs are acceptable when weighed against the risk of a spill that could poison the largest surface freshwater system on the continent.
What to watch next
The tunnel project remains the central point of contention. Enbridge has secured state and federal permits, but legal challenges from environmental groups continue. The timeline for construction, if it proceeds, would run for years.
In the meantime, the pipeline continues to operate under the Straits, carrying its daily volume of oil and natural gas liquids through the most vulnerable point on the Great Lakes. The detail that matters for anyone watching this story is that the debate is not really about engineering.
It is about whether the region’s energy supply chain can be restructured before a failure forces the issue. The Straits of Mackinac are not going anywhere. The currents are not going to change.
The question is whether the pipeline will.
