Michigan Supreme Court Reinforces Public Trust Protections in Line 5 Tunnel Decision

By: W. Dane Carey

On July 31, 2026, the Michigan Supreme Court vacated the Michigan Public Service Commission’s approval of Enbridge Energy’s proposed Line 5 tunnel beneath the Straits of Mackinac and returned the matter to the Commission for further proceedings. In re Application of Enbridge Energy to Replace and Relocate Line 5, Nos. 168335-9 and 168346 (Mich, July 31, 2026). The decision was 6-1, with Justice Welch writing for the majority and Justice Zahra concurring in part and dissenting in part.

The ruling does not finally prohibit construction of the proposed tunnel. It does require the Commission to conduct a more complete analysis of the project’s environmental consequences, available alternatives, and potential effects on resources protected by Michigan’s public trust doctrine.

The decision is significant well beyond the Line 5 controversy. It confirms that Michigan agencies cannot evaluate a project affecting the Great Lakes without separately considering the public’s legally protected interests in those waters and the submerged lands beneath them.

The Proposed Line 5 Tunnel

Line 5 is a petroleum and natural gas liquids pipeline that has operated since 1953. A roughly four-mile segment of the pipeline currently consists of dual pipelines resting on the bottomlands of the Straits of Mackinac, where Lake Michigan and Lake Huron meet.

Enbridge proposed replacing the existing Straits crossing with a new pipeline housed inside a concrete-lined tunnel beneath the lakebed. In December 2023, the Commission approved Enbridge’s application to construct and operate the replacement segment, subject to certain conditions.

Several environmental organizations and four federally recognized Tribal nations challenged that approval. The challengers included For Love of Water (FLOW), the Environmental Law and Policy Center, the Michigan Climate Action Network, the Bay Mills Indian Community, the Grand Traverse Band of Ottawa and Chippewa Indians, the Little Traverse Bay Bands of Odawa Indians, and the Nottawaseppi Huron Band of the Potawatomi. The Tribal challengers raised both statutory claims under the Michigan Environmental Protection Act and arguments grounded in their treaty-protected rights to the waters and fisheries of the Great Lakes.

The Michigan Court of Appeals upheld the Commission’s decision. The Michigan Supreme Court concluded that both the Commission’s analysis and the Court of Appeals’ review were legally insufficient.

The Commission’s Environmental Review Was Too Narrow

One of the principal questions before the Court was how broadly the Commission was required to evaluate the tunnel project under the Michigan Environmental Protection Act (MEPA). MEPA requires courts and administrative agencies to consider whether proposed conduct is likely to pollute, impair, or destroy Michigan’s air, water, or other natural resources. When such environmental harm is established, the decision-maker must also consider whether a feasible and prudent alternative is available.

The Court identified two significant deficiencies in the Commission’s review.

First, the Commission did not adequately determine whether construction of the tunnel would extend the operational life of Line 5 and thereby cause additional environmental consequences. The relevant inquiry was not limited to the immediate physical construction of the tunnel. The Commission was also required to consider environmental effects that could factually and proximately result from the project, including the continued operation of the pipeline that the tunnel would enable.

Second, the Commission did not evaluate alternatives consistently. The majority found that the Commission assessed the risks of the proposed tunnel under one set of assumptions while applying materially different assumptions to competing alternatives, such as rail transport. That kind of asymmetry prevents a meaningful comparison of environmental costs and practical consequences across the available options.

These conclusions reinforce an important feature of MEPA: environmental review must address the reasonably foreseeable consequences of an agency’s decision, not merely the project’s most narrowly defined components.

Public Trust Resources Require Separate Consideration

The Court’s treatment of the public trust doctrine may prove to be the decision’s most lasting contribution to Michigan environmental and water law.

Under Michigan’s public trust doctrine, the State holds navigable waters and the submerged lands beneath them in trust for the benefit of the public. The doctrine protects interests traditionally associated with those waters, including navigation, fishing, boating, and other lawful uses.

The Court rejected the conclusion that the Commission lacked authority to consider those interests. Instead, it held that MEPA requires separate consideration of harm to public trust resources. General consideration of environmental effects is not necessarily a substitute for examining whether a project will interfere with legally protected public rights in navigable waters and submerged lands. When an agency authorizes activity affecting the Great Lakes, it must identify the relevant public trust resources and meaningfully evaluate the potential harm to them.

On this point, the decision was effectively unanimous. Even Justice Zahra’s partial dissent agreed that the Commission failed to consider impacts on public use rights in the Great Lakes.

The Court Clarified the Standard of Judicial Review

The Court concluded that the Court of Appeals had applied an overly deferential standard when reviewing the Commission’s decision. Although courts ordinarily give appropriate consideration to an agency’s factual findings and technical expertise, questions concerning the proper interpretation and application of Michigan law remain subject to meaningful judicial review. Deference does not permit a court to overlook an agency’s failure to apply the governing legal framework.

This portion of the decision matters for parties appearing before state agencies. An administrative record must demonstrate not only that the agency gathered evidence, but also that it applied the correct legal standards, considered the legally required factors, and adequately explained its reasoning.

What the Decision Means in Practice

The Court did not order Line 5 shut down, and it did not permanently prohibit the proposed tunnel. It set aside the Commission’s prior approval and returned the case for additional proceedings. The Commission must now reconsider the project under the legal standards identified by the Court, including whether the tunnel would extend Line 5’s operational life and produce additional environmental harm, whether the proposed project and its alternatives have been compared on a consistent basis, how the project may affect public trust resources in the Straits of Mackinac, and whether the environmental and public trust consequences are permissible under Michigan law.

The tunnel project also remains subject to other state and federal permitting processes. The Court’s ruling concerns the Commission’s approval under Act 16 and MEPA and should not be confused with separate litigation concerning the existing pipeline, the 1953 easement, or permits administered by other agencies, including the ongoing state and federal proceedings over Governor Whitmer’s 2020 shutdown order.

Broader Significance for Michigan Property and Environmental Law

Although Line 5 is an unusually large and controversial project, the legal principles applied by the Court have broader relevance. Michigan agencies regularly make decisions affecting wetlands, shorelines, inland lakes, rivers, Great Lakes bottomlands, public access, utility infrastructure, and private development. This decision confirms that agencies must identify the full scope of their statutory responsibilities before granting approval.

For property owners, municipalities, developers, environmental organizations, and members of the public, the decision carries several practical lessons. An agency’s characterization of a project does not necessarily determine the proper scope of environmental review, because indirect but reasonably foreseeable consequences may also require consideration. An alternatives analysis must be evenhanded, with agencies applying consistent assumptions across the preferred proposal and competing options. Public trust rights are legally distinct interests, and when navigable waters or submerged lands are affected, an agency may need to address those rights separately from general environmental impacts. Finally, a complete administrative record is essential, and parties should identify environmental, public trust, and alternatives issues during the agency proceedings rather than waiting for judicial review.

Michigan’s Public Trust Doctrine Remains a Meaningful Limitation on Government Action

The Court’s decision confirms that the public trust doctrine is not merely a statement of policy. It imposes substantive obligations when the State considers allowing private activity that may affect public rights in Michigan’s navigable waters and submerged lands.

For the Line 5 tunnel, the immediate result is further administrative review. For Michigan water law more broadly, the decision reinforces a principle that property owners, agencies, and practitioners should take seriously: state agencies entrusted with decisions affecting the Great Lakes must account for the public interests the State is legally obligated to protect.

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Carey Jaskowski PLC represents property owners, associations, businesses, and other clients in matters involving Michigan water law, riparian rights, environmental regulation, public access, submerged lands, and administrative proceedings. For guidance regarding a matter affecting Michigan’s land or water resources, contact our office to schedule a consultation.

This article is for informational purposes only and does not constitute legal advice. Environmental and public trust questions are highly fact-specific, and anyone facing a specific issue should consult qualified legal counsel.