Corrected Sept. 10, 2026: The headline now says the Michigan Supreme Court vacated the tunnel’s state siting approval. EGLE’s and the DNR’s permits still stand. This version also corrects the lease status in the scoreboard, attributes the 2024 completion target to Enbridge, gives IEEFA’s cost estimate as a floor, and adds EGLE’s Sept. 9 decision to re-review its permit.
On August 12 the U.S. Army Corps of Engineers signed a Record of Decision granting Enbridge a federal permit to bore a tunnel under the Straits of Mackinac. Twelve days earlier, on July 31, the Michigan Supreme Court vacated the state siting approval the same tunnel needs before anyone can dig. Both are true at once.
What the Corps actually permitted
The Corps’ Detroit District issued a Standard Individual Permit under Section 10 of the Rivers and Harbors Act and Section 404 of the Clean Water Act, file LRE-2010-00463-56-A19. The Record of Decision describes a 3.9-mile tunnel about 21 feet in inside diameter, 3.7 miles of it in bedrock, with 0.79 acres of permanent wetland fill. It runs 54 pages and is posted on the Corps’ project site.
Two things the permit does not do. It does not replace Line 5. The line is 645 miles long, from Superior, Wisconsin to Sarnia, Ontario, and at the Straits it splits into twin 20-inch pipes on the lakebed for a crossing Enbridge and EGLE put at 4.5 miles. The only part of Line 5 the tunnel would hold is the replacement for that stretch. The 2018 agreement also leaves room in it for other utilities, such as electric and broadband cables.
It also sets no construction date. When Enbridge signed its 2018 tunnel agreement with the state, the company targeted completion by 2024. The state’s 2021 wetlands permit expired, in EGLE’s words, “because construction has not yet begun.”
What the Michigan Supreme Court took away
The Public Service Commission approved the tunnel’s siting in December 2023. On July 31, 2026 the Michigan Supreme Court vacated that order 6 to 1 and sent it back. The majority opinion, by Justice Welch, held that “to accurately assess the environmental consequences of the Replacement Project, the PSC should have determined whether the project would be the proximate cause of Line 5’s continued operation and its alleged attendant harms.” Justice Zahra, dissenting in part, called that conclusion “poorly reasoned and illogical.”
That is not the same as killing the project. Enbridge’s application stays in front of the commission, which has to redo the analysis. Until it does, the tunnel has a federal permit and no valid state siting approval.
The tribes did not walk out of consultation
Seven federally recognized tribes held Cooperating Agency roles in the federal review. On March 21, 2025 six of them, Bay Mills, Little River Band, Sault Ste. Marie Tribe, Grand Traverse Band, Match-E-Be-Nash-She-Wish Band and Nottawaseppi Huron Band, sent the Corps a withdrawal letter. Little Traverse Bay Bands of Odawa Indians withdrew five days later. The Record of Decision counts all seven.
The letter is widely described as the tribes quitting consultation. It says the reverse. The withdrawal “applies only to the Tribal Nations’ role as Cooperating Agencies in the NEPA process,” and “the Tribes will continue, for the time being, to engage with the Corps as sovereign Tribal Nations and consult in the Section 106 process.” What they refused was to lend their names to the review, being “no longer willing to expend their time and resources as Cooperating Agencies just so their participation may be used by the Corps to lend credibility to a flawed” impact statement.
After the permit issued, Bay Mills President Whitney Gravelle called it “a profound breach of the United States’ treaty trust responsibility to Tribal Nations.”
September: a letter from the governor and a challenge from four tribes
On Sept. 9 Gov. Gretchen Whitmer wrote to Enbridge president Gregory Ebel and asked the company to “Develop a planned, orderly transition that protects Michigan families and businesses and gets oil out of the Straits.” She urged a shutdown within months, and called the line “a ticking time bomb in the heart of the Great Lakes.”
The same day, EGLE said it would re-examine the permits it issued on July 15. This is the part worth being precise about, because the headlines were not: the permits were not revoked. The agency is re-reading them, and it is the permit’s own conditions that stop work in the meantime. “Until all those legal questions are resolved, conditions in EGLE’s permit prevent construction of the tunnel entrance from moving forward,” said department director Phil Roos.
A day later, on Sept. 10, four Michigan tribes asked EGLE for an administrative hearing to overturn that July 15 water resources permit. If the request is granted, an administrative judge hears evidence before deciding whether the permit stands. “It is time for Michigan to right this wrong by honoring its commitments to Tribal Nations and choosing a future that protects our waters rather than locking us into future generations of risk,” said Whitney Gravelle, president of the Bay Mills Indian Community.
Enbridge has not moved off its position. “We continue to stand ready to meet with the Governor to look at ways that protect Michigan’s natural resources while ensuring the continued safe operation of critical energy infrastructure,” spokesman Ryan Duffy said.
The permit scoreboard
| Approval | Who issues it | Status |
|---|---|---|
| Section 404 / Section 10 permit | Army Corps, Detroit District | Issued Aug. 12, 2026 |
| Wetlands and submerged lands permit (Parts 303, 325) | Michigan EGLE | Reissued July 15, 2026 after the 2021 permit expired. Under state re-review since Sept. 9. Four tribes filed for a contested-case hearing on Sept. 10 |
| Endangered species permit (Part 365) | Michigan DNR | Issued July 15, 2026 |
| Wastewater discharge permit MI0060278 | Michigan EGLE | Pending; comments closed June 30. EGLE expects a decision by the end of September |
| Act 16 siting approval | Michigan Public Service Commission | Vacated July 31, 2026, remanded |
| Tunnel agreement | Mackinac Straits Corridor Authority | Signed December 2018. The 99-year lease starts only after the finished tunnel is accepted |
Two numbers we are not printing
The cost. Enbridge’s site still says “$500M+.” A January 2025 analysis by the Institute for Energy Economics and Financial Analysis says it is “probably reasonable to presume” the project will cost $1.5 billion or more. Either can be quoted with its owner attached. Neither is settled.
The spill count. Enbridge says the Straits crossing has never leaked, and that claim covers only the Straits crossing, not the 645-mile line. In a 2017 count, the National Wildlife Federation, working from federal incident data, found at least 29 spills and more than a million gallons along the line since 1968. Both figures belong to whoever is making them.
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Last verifiedSep. 10, 2026
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Verification note: Corrected Sept. 10, 2026. The headline now says the Michigan Supreme Court vacated the tunnel's state siting approval; EGLE's and the DNR's permits still stand. This version also corrects the tunnel agreement's lease status (the 99-year lease begins only after the finished tunnel is accepted), notes that the 2018 agreement lets other utilities use the tunnel, attributes the 2024 completion target to Enbridge, quotes IEEFA's cost estimate as a floor, and adds EGLE's Sept. 9 decision to re-review its permit. Every source below was checked Sept. 10, 2026.
Primary sources
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Record of Decision, Standard Individual Permit LRE-2010-00463-56-A19 (Enbridge Line 5 Tunnel) — U.S. Army Corps of Engineers, Detroit District
Accessed Sep. 10, 2026. U.S. government work.
The document carries no printed date on its opening pages; the Corps' Aug. 12 release (next row) dates the permit.
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Corps of Engineers issues Enbridge Energy permit for regulated activities proposed for the Line 5 tunnel — U.S. Army Corps of Engineers, Great Lakes and Ohio River Division
Published Aug. 12, 2026. Accessed Sep. 10, 2026. U.S. government work.
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In re Application of Enbridge Energy, Limited Partnership (Michigan Supreme Court opinion, July 31, 2026) — Michigan Supreme Court (slip opinion as posted by Bridge Michigan)
Published Jul. 31, 2026. Accessed Sep. 10, 2026. Court opinion (public domain).
Copy of the court's slip opinion hosted by Bridge Michigan.
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Notice of Withdrawal as Cooperating Agencies, Line 5 Tunnel Project EIS — Bay Mills Indian Community and five other tribal nations (hosted by Earthjustice)
Published Mar. 21, 2025. Accessed Sep. 10, 2026.
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Tribes Slam U.S. Army Corps for Approving Line 5 Tunnel — Earthjustice (joint release with Bay Mills Indian Community)
Published Aug. 12, 2026. Accessed Sep. 10, 2026.
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EGLE reissues resource permit for proposed Mackinac Straits tunnel — Michigan Department of Environment, Great Lakes, and Energy
Published Jul. 15, 2026. Accessed Sep. 10, 2026.
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Line 5: applicable permits — Michigan Department of Environment, Great Lakes, and Energy
Accessed Sep. 10, 2026.
The permit covers wastewater from both construction and operation of the tunnel.
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DNR issues Line 5 permit with conditions to protect natural resources — Michigan Department of Natural Resources
Published Jul. 15, 2026. Accessed Sep. 10, 2026.
Supports: Supports: the DNR issued the tunnel's endangered species permit under Part 365 on July 15, 2026.
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Mackinac Straits Corridor Authority FAQs — Michigan Department of Transportation
Accessed Sep. 10, 2026.
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About Line 5 — Enbridge
Accessed Sep. 10, 2026.
EGLE's Line 5 overview also gives 4.5 miles.
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Line 5 and the Great Lakes Tunnel — Enbridge
Accessed Sep. 10, 2026.
Supports: Supports: Enbridge's site still describes the tunnel as a "$500M+" private investment.
Additional reporting
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Six tribes withdraw from federal talks over Line 5 tunnel permit — Interlochen Public Radio
Published Mar. 26, 2025. Accessed Sep. 10, 2026.
The Corps' Record of Decision (first row) confirms all seven withdrawals.
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State regulators to review issued Line 5 tunnel permits after MI Supreme Court ruling — Interlochen Public Radio
Published Sep. 9, 2026. Accessed Sep. 10, 2026.
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Enbridge should consider closing its old, troubled Line 5 pipeline — Institute for Energy Economics and Financial Analysis
Published Jan. 7, 2025. Accessed Sep. 10, 2026.
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Line 5 Oil Pipeline System Spanning Michigan Has Had 29 Known Spills — National Wildlife Federation
Published Apr. 24, 2017. Accessed Sep. 10, 2026.
NWF dates the count from 1968.
Photo and media credits
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Mackinac Bridge from the air3.jpg (featured image) — Justin Billau, via Wikimedia Commons
Featured image record. Accessed Sep. 10, 2026. CC BY 2.0.
Supports: Featured image, credited on the page as "Photo: Justin Billau, CC BY 2.0, via Wikimedia Commons."
Photographed June 20, 2010. Resized for the site.
