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For more than a decade, controversy over an oil pipeline that passes directly through a Native American reservation and then across a sensitive waterway that is also a key shipping lane has brewed in Wisconsin and Michigan.

Since taking office in January 2025, the Trump administration has joined an already complex fray, with policy decisions and legal filings as well as administrative and judicial appointments that have shifted the strategies and potential outcomes of the situation. The changes affect not just pipeline operator Enbridge but also the environmental, Indigenous and political leaders working to shut down the pipeline, known as Line 5.

Part of the dispute is slated to come before the U.S. Supreme Court in the coming months, but that will not deliver the final resolution of the situation.

I am a water policy and politics analyst and a former gubernatorial appointee to Michigan's Pipeline Safety Advisory Board. I see these controversies raising critical questions about the environmental and economic future of the Great Lakes region and serving as a proxy for wider national battles over water policy, Indigenous rights and the role of fossil fuels in the nation's future.

Built in 1953, Enbridge's Line 5 oil pipeline carries petroleum products mostly from western Canada's tar sands to refineries in eastern Canada, using the Great Lakes as a shortcut. It traverses 645 miles (1,040 km) through Wisconsin and Michigan and transports approximately 23 million gallons of oil and natural gas liquids per day from Superior, Wisconsin, to Marysville, Michigan, and then across the Saint Clair River to Sarnia, Ontario.

The pipeline has been the subject of intense scrutiny since soon after a 2010 oil spill into the Kalamazoo River in Michigan from another Enbridge pipeline with a similar start and endpoint. The 2012 publication of Sunken Hazard, a report from the National Wildlife Federation about the potential for a spill from Line 5, fomented public concern and launched an advocacy movement that began with questions about Line 5's safety and has led to calls for its complete shutdown.

While the entire pipeline is being scrutinized, there are two primary areas of concern. In Wisconsin, the pipeline runs for 12 miles (19 km) across the reservation of the Bad River Band of Lake Superior Chippewa. And when it crosses from Michigan's Upper Peninsula to its Lower Peninsula, the line splits into two parallel pipes that run along the bottom of the Straits of Mackinac, which connect Lake Michigan and Lake Huron.

In 2021, Michigan Gov. Gretchen Whitmer revoked Enbridge's easement to operate the pipeline across the Straits of Mackinac. The governor asserted that Enbridge "repeatedly violated the 1953 easement and that the continued operation of the dual pipelines violates the state's solemn duty to protect the Great Lakes."

Some of her concerns exist because the pipeline sits in the open water of the Great Lakes and has been damaged multiple times by ship's anchors, is subject to corrosion, and has been found to be bent and deformed by the extremely powerful currents in the Straits of Mackinac.

Enbridge refused to comply with the shutdown order and has taken the battle into the courts while continuing to send petroleum products through the pipeline across the straits. The Trump administration - through a Sept. 19, 2025, court filing - is supporting Enbridge's claim that the pipeline is not subject to state regulation and oversight.

There has been a long back-and-forth about whether state courts have jurisdiction, as state officials argued, or whether federal courts should handle it, as Enbridge claimed. In June 2025 the trial was set for a state court when the U.S. Supreme Court unexpectedly stepped in at Enbridge's request. The case has not yet been scheduled for oral arguments before the court, but they - and a potential ruling - are expected sometime between October 2025 and June 2026.

The state court has said it will continue its proceedings without waiting for a Supreme Court decision. But the ground is set for the continuation of an extended and complicated legal battle.

While Enbridge is fighting the shutdown of its existing pipeline, the company is seeking state and federal permission to build a replacement, by digging a new tunnel below the Straits of Mackinac.

The company needs both federal and state permits before construction can begin. The federal permits are expected to come quickly as a result of a Trump administration policy.

On the first day of his second term, Trump declared a "national energy emergency." In general, the policy is being used to try to slow the transition away from fossil fuels and toward clean energy sources, and to remove climate change as a factor in environmental reviews and permitting.

For Line 5, the most consequential provisions of the order are those that call for "emergency approvals" and "expediting the Delivery of Energy Infrastructure." The tunnel is on the Army Corps of Engineers' list of projects eligible for fast-track approval.

However, Enbridge still needs state permits, which many groups are opposing based on potential environmental damage to the shoreline, the safety of the tunnel and the need to address climate change by slowing down oil extraction.

In addition, all of the federally recognized tribal governments in Michigan oppose Line 5's continued existence, contending that Indigenous fishing rights in the Straits of Mackinac are at risk from the pipeline both ecologically and culturally. Their position, expressed in a state-court challenge to the tunnel, could end up testing the power of their rights under treaties with the U.S. government.

In addition to both of those disputes, a Native American tribe in Wisconsin undertook its own efforts to reduce the risk of environmental damage from the pipeline on its land and the surrounding watershed.

In 2013, the Bad River Band declined to renew Enbridge's pipeline easement through its territory, which is sometimes referred to as the "Everglades of the Great Lakes" because of its extensive and pristine wetlands. In 2017 the tribe voted to require Enbridge to remove the line from its land.

Enbridge refused to comply and has contested the validity of the Bad River Band's decision, inherently challenging the tribe's sovereignty. At the same time, the company is attempting to reroute the pipeline around the reservation - though still within the Bad River watershed.

In 2019 the tribe sued Enbridge to force the removal and ultimately won a federal judge's ruling that the company must remove the pipeline by June 2026 and pay US$5.15 million for ongoing trespassing. Enbridge has appealed, and many observers expect that case to also come to the Supreme Court.

As that process unfolds, Enbridge is seeking expedited state and federal permits for the reroute. Environmental advocates, tribe members and others have asked a court to decide whether state permits that were granted in late 2024 were given without following the proper procedure. Hearings on that question continue.

Pipeline opponents are also asking the Army Corps of Engineers, which must issue its own permits, to reject the application for the new route, effectively cutting off the pipeline. However, this federal permit is also subject to Trump's "national energy emergency," and so it is unlikely to be stopped by federal agencies and is expected by the end of 2025.

On all three parallel fronts, the Trump administration's shaping of policy and the judiciary has put advocates on the defensive.

The state of Michigan is concerned that its autonomy over its portion of the Great Lakes is at risk if the federal government and courts can overrule its revocation of Enbridge's easement to operate.

Native American governments are concerned that their treaty-guaranteed fishing and land rights will be sacrificed in service of an energy company's interests.

And, of course, Line 5 has major implications for Great Lakes protection and mitigating climate change, where the Trump administration has tilted the playing field in favor of fossil fuels and away from clean energy and environmental protection.

Yet the outcomes are not at all clear, and Enbridge would likely have to win on all fronts to avoid the pipeline being shut down, since it cannot operate the pipeline if any segment is inoperable. I expect the implications of Line 5's ultimate fate to reverberate across the country for years to come.