Why It Matters
The Army Corps of Engineers’ approval of Enbridge’s Line 5 tunnel project clears a major federal hurdle for a $500 million infrastructure undertaking designed to reduce the risk of oil and natural gas spills in the Great Lakes. The decision resolves a years-long permitting dispute but faces legal challenges from tribal nations and environmental opponents who argue the review process was flawed.
What Happened
The U.S. Army Corps of Engineers issued a permit authorizing Enbridge to construct a four-mile tunnel beneath the Straits of Mackinac to replace the existing dual pipelines running across the lake bed. The Line 5 corridor carries crude oil and natural gas liquids from Superior, Wisconsin, to Sarnia, Ontario, serving refineries throughout the Midwest and Eastern Canada.
The tunnel project aims to eliminate the risk of ruptures and spills by burying the pipeline segment beneath the straits’ lake bed rather than leaving it exposed on the surface, where it has been vulnerable to anchor strikes and other damage. The current configuration consists of two 4.5-mile pipelines that have operated since the 1950s.
The permitting process has been contentious. Seven tribal nations withdrew as cooperating agencies before the Corps issued its decision, signaling their opposition to the project. On July 31, the Michigan Supreme Court ordered the state’s Public Service Commission to reconsider its tunnel permit, finding that the commission had failed to evaluate alternative routes and had improperly limited the scope of its environmental review.
The Corps completed its environmental review on an accelerated timeline following a 2025 Trump executive order directing federal agencies to expedite permitting for critical energy infrastructure. Lt. Col. Donald K. Lew, the Corps’ Detroit District Commander, stated that “the approval of the Enbridge Line 5 tunnel permit application is the culmination of a robust and thorough evaluation process.”, as first reported by the Michigan Advance
By the Numbers
4.5 miles — current length of dual pipelines in the Straits of Mackinac
Four miles — proposed length of replacement tunnel segment
Six years — duration of the Corps’ environmental review process
July 31 — date the Michigan Supreme Court ruled the state’s Public Service Commission must revisit its tunnel permit decision
Zoom Out
The Line 5 approval reflects a broader national tension over energy infrastructure modernization and environmental protection. The 2010 Kalamazoo River oil spill from an Enbridge Line 6B rupture killed wildlife and contaminated a 40-mile stretch of waterway, establishing a precedent cited by project opponents. Multiple anchor strikes on Line 5 in recent years have heightened safety concerns among environmental and tribal advocates, though Enbridge maintains its safety record.
Federal energy infrastructure permitting has accelerated under the current administration’s push to streamline reviews, contrasting with the slower multi-year processes that characterized the previous decade. The Line 5 decision follows similar expedited approvals for other pipeline and electrical transmission projects deemed vital to national energy supply.
What’s Next
Tribal nations and environmental groups are expected to pursue legal challenges to the Corps permit. The Michigan Public Service Commission must address the state Supreme Court’s July 31 ruling and reconsider its own tunnel permit decision. Enbridge has not announced a timeline for tunnel construction, though the federal permit removal clears a critical regulatory barrier to the project’s advancement.