In Re APPLICATION OF ENBRIDGE ENERGY TO REPLACE AND RELOCATE LINE 5

Michigan Supreme Court Lansing, Michigan Syllabus Chief Justice: Justices: Megan K. Cavanagh Brian K. Zahra Richard H. Bernstein Elizabeth M. Welch Kyra H. Bolden Kimberly A. Thomas Noah P. Hood This syllabus constitutes no part of the opinion of the Court but has been Reporter of Decisions: prepared by the Reporter of Decisions for the convenience of the reader. Kimberly K. Muschong In re APPLICATION OF ENBRIDGE ENERGY TO REPLACE AND RELOCATE LINE 5 Docket Nos. 168335, 168336, 168337, 168338, 168339, and 168346. Argued March 16, 2026 (Calendar Nos. 2 and 3). Decided July 31, 2026. These consolidated appeals involve the intersection of three legal frameworks—1929 PA 16 (Act 16), MCL 483.1 et seq. (giving the PSC primary authority to regulate pipelines in Michigan); Michigan’s environmental protection act (MEPA), MCL 324.1701 through MCL 324.1706; and the common-law public trust doctrine—and the order of the Michigan Public Service Commission (PSC) approving Enbridge Energy Limited Partnership’s application to construct a tunnel under the Straits of Mackinac to house a portion of its Line 5 pipeline (the “Replacement Project”). The PSC granted Enbridge’s predecessor approval to construct Line 5 in 1953, and the Michigan Conservation Commission also granted it an easement to construct two 20-inch pipes (referred to as the dual pipelines) located on or suspended above the lakebed across the Straits. As part of a negotiated agreement between the state and Enbridge in 2017 through 2018, the Replacement Project contemplated the decommissioning of the dual pipelines and the construction of a concrete-lined tunnel under the Straits’ lakebed and a new 30-inch pipe through the tunnel. In 2018, the Legislature created the Mackinac Straits Corridor Authority (MSCA) and authorized it to enter into an agreement to build a “utility tunnel” under the Straits. The Department of Natural Resources granted the MSCA an easement to construct a tunnel under the Straits, and once Enbridge completes the tunnel, the MSCA will take ownership of the tunnel and provide Enbridge with a 99-year lease. After Enbridge filed its application for the Replacement Project with the PSC, appellants, Bay Mills Indian Community, Grand Traverse Band of Ottawa and Chippewa Indians, Little Traverse Bay Bands of Odawa Indians, Nottawaseppi Huron Band of the Potawatomi, Environmental Law and Policy Center, Michigan Climate Action Network, and For Love of Water, intervened in the proceedings to oppose the Replacement Project. Appellees Michigan Laborers’ District Council, Michigan Propane Gas Association, and National Propane Gas Association intervened to support the project. The PSC referred the matter to an administrative law judge (ALJ) to conduct proceedings and build a record. Relevant to this appeal, the parties disputed the proper scope of the PSC’s analysis under MEPA. Enbridge filed a motion in limine seeking to exclude as legally irrelevant various issues from the PSC’s consideration, including the construction of the utility tunnel, the environmental impact of the tunnel construction, the public need for and continued operation of Line 5, the current operational safety of Line 5, whether Line 5 has an adverse impact on climate change, and the intervening parties’ climate change agendas. The ALJ granted the motion as to all issues other than the construction of the utility tunnel, and several intervenors appealed the ruling to the PSC. While that appeal was pending, Governor Gretchen Whitmer issued a notice of revocation of the 1953 easement. The PSC remanded the case to the ALJ to consider the impact of the Governor’s actions. On remand, the ALJ reached the same conclusions as he had before. He found that the PSC’s 1953 order had already established that Line 5 served a public need and that this finding had no expiration date. The ALJ further concluded that Governor Whitmer’s actions could not “be used to expand the scope of this case to include an examination or determination of the public need for Line 5, or any aspect of its operation and safety.” The intervenors again appealed, and the PSC largely affirmed the ALJ’s ruling. Like the ALJ, the PSC determined that its 1953 decision approving Line 5, as well as earlier Supreme Court caselaw, established that the pipeline complied with Act 16 and that there was no expiration date for this finding. Accordingly, it concluded that the Act 16 analysis in this case should be limited to the Replacement Project and not the pipeline as a whole. The PSC limited its MEPA analysis “to the conduct at issue in this case,” i.e., the Replacement Project, and refused to consider evidence of potential pollution, impairment, and destruction of Michigan’s natural resources resulting from existing sections of Line 5, including the danger of oil spills. It also concluded that its MEPA analysis did “not extend to the entirety of Line 5,” but was limited to the single new pipeline and tunnel. However, the PSC also determined that the conduct at issue included the products flowing through the new pipeline section and allowed the introduction of evidence of the greenhouse gas emissions that would result from the consumption of the products. The PSC also concluded that greenhouse gases were “pollution” within the meaning of MEPA and that although the Replacement Project was limited to the 4-mile section of the pipeline described in the application, MEPA review was necessary because that pipeline section would involve hydrocarbons that may result in pollution. After the presentation of additional evidence and testimony, the ALJ closed the record and transferred the case to the PSC for a final decision. The PSC issued an order granting Enbridge approval under Act 16 to construct the Replacement Project. It found that the requirements of both Act 16 and MEPA were satisfied and that there were no feasible or prudent alternatives to the Replacement Project, but it declined to consider the public trust doctrine in its analysis. Appellants appealed the PSC’s ruling to the Court of Appeals. In a published per curiam opinion, the Court of Appeals, M. J. KELLY, P.J., and LETICA and WALLACE, JJ., affirmed. ___ Mich App ___ (February 19, 2025) (Docket Nos. 369156, 369157, 369159, 369161, 369162, 369163, 369165, and 369231). Appellants sought leave to appeal, and the Supreme Court granted the applications. ___ Mich ___; 25 NW3d 327 (2025) (Docket Nos. 168335 to 168339); ___ Mich ___; 25 NW3d 319 (2025) (Docket No. 168346). In an opinion by Justice WELCH, joined by Chief Justice CAVANAGH and Justices BERNSTEIN, BOLDEN, THOMAS, and HOOD, the Supreme Court held:  Courts must review de novo an agency’s application of MEPA, regardless of whether a case commences in court or in administrative proceedings. MEPA requires (1) consideration of the environmental impact factually and proximately caused by the conduct at issue, (2) a fair and reasoned comparison of the environmental impacts of any alternatives to the conduct considered, and (3) consideration of the conduct’s potential effects on public trust resources. The Court of Appeals erred in this case by applying a deferential standard of review to the PSC’s decision, and the PSC erred by (1) failing to consider whether the tunnel project will factually and proximately cause the extension of Line 5’s operational life, potentially resulting in additional environmental harm; (2) comparing alternatives in an inconsistent manner; and (3) failing to consider the project’s impact on public trust resources. 1. The Court of Appeals erred by applying a deferential standard of review to the PSC’s MEPA determination rather than analyzing de novo whether the proposed conduct satisfies MCL 324.1705(2). MEPA decisions are reviewed de novo whether they originate as an administrative proceeding or through direct litigation in court, meaning that the reviewing court must consider the legal issues independently and review the record without deference to prior proceedings. Nothing in MEPA’s text implies the existence of multiple standards of review, and interpreting the provision at issue in this case—MCL 324.1705(2)—to provide for de novo review of administrative agencies’ MEPA determinations is consistent with both the language of MEPA as a whole and MEPA’s purpose of spurring the development of a common law of environmental quality through judicial decisions. The Court previously determined that MCL 324.1704(3) requires a court to independently and nondeferentially review an agency decision after remitting a case to that agency for administrative proceedings, and there is no meaningful difference between MCL 324.1704(3) and MCL 324.1705(2). Regardless of how a MEPA case originates, the task for the trial court—or agency—is the same. It must adjudicate or determine whether the “conduct” at issue is likely to pollute, impair, or destroy the air, water, or other natural resources or the public trust in these resources. 2. Under MEPA, harms asserted beyond the conduct itself must be examined to determine if they are factually and proximately caused by the conduct. In this case, the PSC must apply this framework and determine whether the Replacement Project will factually and proximately cause Line 5’s extended lifespan and attendant harms. In applying MEPA, the factfinder must first define the “conduct” at issue. “Conduct” under MEPA is distinguishable from alleged environmental harms. In citizen MEPA suits, the allegations in the plaintiff’s complaint define the conduct at issue. In administrative proceedings— whether initiated by an agency under MCL 324.1705(2) or remitted to an agency by the court under MCL 324.1704(2)—the subject of the proceedings is the conduct at issue under MEPA. Here, the Replacement Project for which Enbridge sought approval in its Act 16 application was the subject of the PSC proceedings. Once the relevant “conduct” is established, MEPA requires courts and agencies to determine or adjudicate whether the conduct will cause pollution, impairment, or destruction of the air, water, or other natural resources, or the public trust in these resources. This analysis can be broken into two steps: (1) determining which harms are at issue and (2) assessing the scope of those harms. At the first step, the factfinder—aided by the parties—must determine what kind of environmental risks the conduct in question poses. Under MCL 324.1705(1) and (2), the focus is on those harms that are likely effects of the conduct. Although this concept appears broad, MEPA’s text limits its scope by requiring both factual causation (i.e., the harm is an “effect” of conduct) and proximate causation (i.e., the harm is “likely”). Proximate cause requires more than speculation or conjecture, and a mere possibility is not enough to establish either but-for causation or proximate causation. Determining the harm of the relevant conduct is a factually intensive inquiry and does not lend itself to hard-and-fast rules; courts and agencies must use common sense and apply basic proximate cause principles. A factfinder should not fully quantify the effects of a risk until it determines that the risk is a result of the proposed conduct. This analysis therefore necessitates a case-by-case inquiry that allows the courts to fashion standards in the context of actual problems as they arise in individual cases. Once the factfinder has determined which environmental risks are actually relevant to the conduct, it must carry out its statutory duty to adjudicate or determine the impact of the defendant’s conduct on the air, water, or other natural resources, and on the public trust in these resources. If the factfinder determines that the conduct at issue poses no meaningful environmental harm, the analysis ends, but if the factfinder determines that the environmental harms are the likely effects of the conduct at issue, the factfinder may not permit the conduct if a feasible and prudent alternative exists. 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. Because it did not do so, the PSC was unable to fulfill its obligations under MEPA to determine, pursuant to MCL 324.1705(2), what pollution, impairment, or destruction of the air, water, or other natural resources, or the public trust in these resources, the project might cause; that is, the PSC erred by not examining whether the Replacement Project would be the proximate cause of further environmental harms by extending Line 5’s lifespan. For purposes of the MEPA harm analysis, Line 5’s continued operation, with and without the Replacement Project, was a factual question, not just a legal one. The PSC also acted inconsistently by considering greenhouse emissions from the pipeline as a whole in its harms analysis, but declining to consider other environmental risks (like oil spills) using that same scope. 3. Once a court or an agency finds that the conduct at issue has polluted, impaired, or destroyed or is likely to pollute, impair, or destroy the air, water, or other natural resources or the public trust in these resources, the next step, as set forth in MCL 324.1705(2), is to determine whether there is a feasible and prudent alternative that avoids or mitigates these environmental effects. Determining the feasibility or prudence of an “alternative” necessarily calls for a benchmark against which the alternative may be evaluated. That benchmark is the harm caused by the proposed conduct. Accordingly, a meaningful examination of the alternatives cannot occur until the impact of the relevant conduct on the air, water, or other natural resources, and on the public trust in these resources, is determined. This analysis of environmental impacts is distinct from the requirements that an alternative be feasible, prudent, and consistent with the public health, safety, and welfare. Accordingly, they may be considered independently, though both bear on the factfinder’s final decision. In addition, MCL 324.1705(2) requires that both the conduct and the alternatives be consistent with the public health, safety, and welfare. The alternatives analysis exists under MEPA to determine if there is a feasible and less environmentally harmful pathway than the challenged conduct. In order for this analysis to accomplish its goals, the environmental impact of the conduct at issue must be compared with that of the alternatives being considered. An analysis that fails to do so will not allow a reasoned choice of alternatives. The inconsistencies in the PSC’s comparisons did not allow for such a “reasoned choice.” The PSC incorrectly compared the environmental effects of alternatives that would fully replace Line 5 with the effects of the Replacement Project alone. 4. MEPA requires separate consideration of harms to public trust resources. The correct way to define “public trust” in MEPA is by looking to the common-law public trust doctrine. The doctrine serves to protect the waters of the Great Lakes and their submerged lands and requires consideration of the public’s right to fish, hunt, travel through, and otherwise utilize the Great Lakes. Just as the MEPA factfinder must assess and mitigate harm to the water and the air, so too must it assess and mitigate harm to public trust resources. The PSC erred by failing to determine whether the Replacement Project would pollute, impair, or destroy public trust resources. Court of Appeals judgment reversed, PSC order vacated, and case remanded to the PSC for further proceedings. Justice ZAHRA, concurring in part and dissenting in part, concurred in the majority opinion limited only to the holding that the matter should be remanded to the PSC for express findings on the issue of public trust; otherwise, he disagreed with the conclusions reached in the majority opinion in several respects. First, the majority opinion errs by concluding that appellate courts review de novo administrative decisions under MEPA. The majority opinion does not provide the PSC’s decision any degree of deference even though some level of deference is generally afforded to administrative decision-makers because of their expertise in the regulated field. MCL 324.1705(2) plainly contemplates judicial review but does not describe the judicial review required. However, Const 1963, art 6, § 28, requires reviewing courts to determine whether agency orders are authorized by law and supported by competent, material, and substantial evidence on the whole record. Applying de novo review in this case allows the majority to dismiss the PSC’s determinations or even substitute its own beliefs for the PSC’s findings. The majority opinion also ignores the clear differences in the text of MCL 324.1701 and MCL 324.1705 to erroneously conclude that the Legislature did not intend for the MEPA standard to differ between citizen suits and administrative proceedings. Justice ZAHRA further disagreed with the majority opinion’s expanded scope of analysis under MEPA. The majority opinion’s conclusion—that the continued operation of Line 5 is itself a relevant adverse environmental effect of the Replacement Project—is poorly reasoned and illogical, and it creates a moral hazard. By dismissing the PSC’s determination and expanding the scope of review to the entirety of Line 5, the majority opinion ignores that Line 5 has already been determined to be in the public interest, and its continued operation is the result of the authority the state granted Enbridge’s predecessor to construct, use, and maintain Line 5, not the Replacement Project. The majority opinion’s interpretation of “likely” effects is particularly problematic; tenuous, remote, or peripheral environmental effects should not be considered relevant in determining feasible alternatives to the Replacement Project. Instead, consideration of proposed feasible alternatives must be limited to alternatives to the Replacement Project, not alternatives to Line 5 as a whole. While the PSC erroneously considered feasible alternatives to the entirety of Line 5, the PSC did properly consider feasible alternatives to the Replacement Project. Finally, while the PSC did not expressly consider the public trust in its final opinion, necessitating remand on that issue, the opinion clearly addressed the substance of the public trust in the state’s natural resources. Justice ZAHRA additionally noted that the Department of Environment, Great Lakes, and Energy recently granted a permit to Enbridge for the Replacement Project, in which proceedings the public trust was expressly considered; this could aid the PSC in independently addressing the public trust on remand.  Michigan Supreme Court Lansing, Michigan OPINION Chief Justice: Justices: Megan K. Cavanagh Brian K. Zahra Richard H. Bernstein Elizabeth M. Welch Kyra H. Bolden Kimberly A. Thomas Noah P. Hood FILED July 31, 2026 STATE OF MICHIGAN SUPREME COURT In re APPLICATION OF ENBRIDGE ENERGY TO REPLACE AND RELOCATE LINE 5. LITTLE TRAVERSE BAY BANDS OF ODAWA INDIANS, Appellant, v No. 168335 MICHIGAN PUBLIC SERVICE COMMISSION, MACKINAC STRAITS CORRIDOR AUTHORITY, MICHIGAN PROPANE GAS ASSOCIATION, NATIONAL PROPANE GAS ASSOCIATION, and MICHIGAN LABORERS’ DISTRICT COUNCIL, Appellees, and ENBRIDGE ENERGY LIMITED PARTNERSHIP, Petitioner-Appellee. In re APPLICATION OF ENBRIDGE ENERGY TO REPLACE AND RELOCATE LINE 5. BAY MILLS INDIAN COMMUNITY, Appellant, v No. 168336 MICHIGAN PUBLIC SERVICE COMMISSION, MACKINAC STRAITS CORRIDOR AUTHORITY, MICHIGAN PROPANE GAS ASSOCIATION, NATIONAL PROPANE GAS ASSOCIATION, and MICHIGAN LABORERS’ DISTRICT COUNCIL, Appellees, and ENBRIDGE ENERGY LIMITED PARTNERSHIP, Petitioner-Appellee. In re APPLICATION OF ENBRIDGE ENERGY TO REPLACE AND RELOCATE LINE 5. GRAND TRAVERSE BAND OF OTTAWA AND CHIPPEWA INDIANS, Appellant, v No. 168337 2 MICHIGAN PUBLIC SERVICE COMMISSION, MACKINAC STRAITS CORRIDOR AUTHORITY, MICHIGAN PROPANE GAS ASSOCIATION, NATIONAL PROPANE GAS ASSOCIATION, and MICHIGAN LABORERS’ DISTRICT COUNCIL, Appellees, and ENBRIDGE ENERGY LIMITED PARTNERSHIP, Petitioner-Appellee. In re APPLICATION OF ENBRIDGE ENERGY TO REPLACE AND RELOCATE LINE 5. NOTTAWASEPPI HURON BAND OF THE POTAWATOMI, Appellant, v No. 168338 MICHIGAN PUBLIC SERVICE COMMISSION, MACKINAC STRAITS CORRIDOR AUTHORITY, MICHIGAN PROPANE GAS ASSOCIATION, NATIONAL PROPANE GAS ASSOCIATION, and MICHIGAN LABORERS’ DISTRICT COUNCIL, Appellees, and 3 ENBRIDGE ENERGY LIMITED PARTNERSHIP, Petitioner-Appellee. In re APPLICATION OF ENBRIDGE ENERGY TO REPLACE AND RELOCATE LINE 5. ENVIRONMENTAL LAW & POLICY CENTER and MICHIGAN CLIMATE ACTION NETWORK, Appellants, v No. 168339 MICHIGAN PUBLIC SERVICE COMMISSION, MACKINAC STRAITS CORRIDOR AUTHORITY, MICHIGAN PROPANE GAS ASSOCIATION, NATIONAL PROPANE GAS ASSOCIATION, and MICHIGAN LABORERS’ DISTRICT COUNCIL, Appellees, and ENBRIDGE ENERGY LIMITED PARTNERSHIP, Petitioner-Appellee. In re APPLICATION OF ENBRIDGE ENERGY TO REPLACE AND RELOCATE LINE 5. 4  FOR LOVE OF WATER, Appellant, v No. 168346 MICHIGAN PUBLIC SERVICE COMMISSION, MACKINAC STRAITS CORRIDOR AUTHORITY, MICHIGAN PROPANE GAS ASSOCIATION, NATIONAL PROPANE GAS ASSOCIATION, and MICHIGAN LABORERS’ DISTRICT COUNCIL, Appellees, and ENBRIDGE ENERGY LIMITED PARTNERSHIP, Petitioner-Appellee. BEFORE THE ENTIRE BENCH WELCH, J. These cases are about the intersection of the Great Lakes, energy transmission, and administrative review. In particular, they concern the order of the Michigan Public Service Commission (PSC) approving appellee Enbridge Energy Limited Partnership’s application to construct a tunnel under the Straits of Mackinac to house a portion of its Line 5 pipeline (the “Replacement Project”). Appellants—environmental advocacy groups and Indian Tribes—contend that the PSC erred in its analysis of the project’s environmental effects under the Michigan environmental protection act (MEPA). 1 1 MCL 324.1701 through MCL 324.1706 (Part 17 of the Natural Resources and Environmental Protection Act (NREPA), MCL 324.101 et seq.). While MEPA was 5  We take this opportunity to answer several questions about MEPA’s scope and function. First, we hold that courts must review de novo an agency’s application of MEPA, regardless of whether a case commences in court or in administrative proceedings. Second, we hold that MEPA requires (1) consideration of the environmental impact factually and proximately caused by the conduct at issue, (2) a fair and reasoned comparison of the environmental impacts of any alternatives to the conduct considered, and (3) consideration of the conduct’s potential effects on public trust resources. Applying these holdings to the cases at issue, we conclude that the Court of Appeals erred by applying a deferential standard of review to the PSC’s decision, and that the PSC erred by (1) failing to consider whether the tunnel project will factually and proximately cause the extension of Line 5’s operational life, potentially resulting in additional environmental harm; (2) comparing alternatives in an inconsistent manner; and (3) failing to consider the project’s impact on public trust resources. Accordingly, we reverse the judgment of the Court of Appeals, vacate the PSC’s order approving the construction of the Replacement Project, and remand this matter to the PSC for further proceedings consistent with this opinion. I. FACTUAL BACKGROUND The Great Lakes are the largest freshwater system on Earth. Department of Environment, Great Lakes, and Energy, Learn About our Great Lakes <https://www.michigan.gov/egle/public/learn/great-lakes> (accessed June 12, 2026) originally enacted as a standalone statute, see 1970 PA 127, it was later recodified—in essentially the same form—as part of NREPA, see 1994 PA 451. For simplicity, we use the current citations for MEPA’s provisions throughout this opinion. 6 [https://perma.cc/7AJU-ZJKS]. “[T]he pure blue waters of these incomparable inland seas” are “Michigan’s great natural resource[.]” Obrecht v Nat’l Gypsum Co, 361 Mich 399, 416; 105 NW2d 143 (1960). Connecting Lake Michigan and Lake Huron, the Straits of Mackinac are a critical point in this ecosystem. As the many Indian Tribes involved in this litigation point out, the Great Lakes and the Straits of Mackinac have nourished life in this region for thousands of years. See generally United States v Michigan, 471 F Supp 192, 221-225 (WD Mich, 1979) (discussing the importance of fishing to the native inhabitants of Michigan in the context of a landmark decision enforcing tribal treaty fishing rights). The Straits, spanned by the Mackinac Bridge, are a significant natural and commercial resource for the state and a point of pride for Michiganders. A. LINE 5’s HISTORY The Line 5 pipeline, operated by Enbridge, is 645 miles long and carries oil and liquid natural gas (LNG) from Superior, Wisconsin, to Sarnia, Ontario. It is part of a larger network of Enbridge pipelines stretching across the United States and Canada. Although Line 5 mostly transports hydrocarbons across Michigan to eastern Canada, the line provides crude oil to a few smaller facilities in Michigan, provides most of the Upper Peninsula’s propane supply, and provides jet fuel to the Detroit Metropolitan Wayne County Airport. In 1953, Enbridge’s predecessor—Lakehead Pipe Line Company, Inc. (Lakehead)—received approval from the PSC to construct the pipeline presently known as 7 Line 5. The Michigan Conservation Commission 2 also granted Lakehead an easement to construct two 20-inch pipes (referred to as the dual pipelines) located on or suspended above the lakebed across the Mackinac Straits. This Court rejected a collateral attack on the PSC’s decision in Lakehead Pipe Line Co, Inc v Dehn, 340 Mich 25; 64 NW2d 903 (1954). In that case, landowners challenging the condemnation of their land along the pipeline’s path argued “that the construction and operation of the pipe line in question here is not a purpose for which the State may grant the power of eminent domain,” as Lakehead primarily contemplated “the transporting of oil from Canadian oil fields to refineries in” Canada. Id. at 36. The Court rejected their argument, noting that Lakehead “propose[d] to deliver oil to Michigan refineries and other purchasers in this State” and holding that “the construction, maintenance and operation of the pipe line in question” would “benefit[] the people of Michigan.” Id. at 36, 38. 3 Appellants allege that the dual pipelines, which have a daily carrying capacity of up to 540,000 barrels and are elevated above the lakebed by supports, are vulnerable to damage. Anchor strikes are a particular concern, as exemplified by an April 2018 strike that dented, but did not rupture, the dual pipelines. 4 Given the fast-moving currents and 2 The Conservation Commission was the predecessor to the Natural Resources Commission. See Westervelt v Natural Resources Comm, 402 Mich 412, 418 n 1; 263 NW2d 564 (1978) (opinion by WILLIAMS, J.). 3 Notably, the pipeline’s approval, construction, and attendant litigation all preceded the adoption in 1963 of Michigan Constitution, Article 4, § 52—which requires the Legislature to “provide for the protection of the air, water and other natural resources of the state”— and the enactment of MEPA in 1970, 1970 PA 127. 4 See National Transportation Safety Board, Marine Accident Brief—Anchor Contact of Articulated Tug and Barge Clyde S VanEnkevort/Erie Trader with Underwater Cables and Pipelines (May 21, 2019), p 7, available at 8 connection of both Lake Michigan and Lake Huron to the Straits, if one of the pipes were to rupture, the resulting spill would be environmentally and economically catastrophic. B. THE REPLACEMENT PROJECT The “Replacement Project” at issue here emerged as a result of a series of agreements negotiated between Enbridge and Governor Rick Snyder on behalf of the state of Michigan in 2017 through 2018. Specifically, the project involves drilling and constructing a new, concrete-lined tunnel through the bedrock approximately 60 feet to 250 feet under the Straits’ lakebed and running a new 30-inch pipe through that tunnel. According to the terms of Enbridge’s agreement with the state, this would allow the dual pipelines to be decommissioned and “would essentially eliminate the risk of adverse impacts that may result from a potential oil spill in the Straits . . . .” The project would not change Line 5’s current carrying capacity or the service it provides. Initially, the project contemplated that the tunnel could be used for other utilities, such as electric and broadband lines. However, the PSC declined to approve this aspect of the project, concluding that “Enbridge failed to demonstrate by a preponderance of the evidence that co-locating third- party utilities in the tunnel with the Straits Line 5 replacement segment is reasonable or safe.” In 2018, the Legislature created the Mackinac Straits Corridor Authority (MSCA) and authorized it to enter into an agreement to build a “utility tunnel” under the Straits. See 2018 PA 359. Enbridge agreed to construct and maintain the tunnel and the <https://www.ntsb.gov/investigations/AccidentReports/Reports/MAB1912.pdf> (accessed June 12, 2026) [https://perma.cc/5DAW-95YV]. 9 replacement pipeline and to deactivate the existing dual pipelines once the Replacement Project becomes operational. For its part, the MSCA agreed to obtain the necessary property rights for Enbridge to construct the Replacement Project. Consistent with this goal, in December 2018, the Department of Natural Resources (DNR) granted the MSCA an easement to construct a tunnel under the Straits. Once Enbridge completes the tunnel, the MSCA will then take ownership of the tunnel and provide Enbridge with a 99-year lease. Enbridge filed an application with the PSC to move forward with the construction. As set forth in more detail below, the PSC approved the application and the Court of Appeals affirmed that decision, resulting in this appeal. II. LEGAL BACKGROUND Some initial legal background is helpful for understanding the proceedings that led to this appeal and the positions the parties have taken. Three legal frameworks intersect in this case: 1929 PA 16 (Act 16), MEPA, and the common-law public trust doctrine. A. ACT 16 We begin with 1929 PA 16 (Act 16), codified at MCL 483.1 et seq., which gives the PSC primary authority to regulate pipelines in this state. Under this framework, pipeline operators must apply to and receive approval from the PSC in order to construct new facilities. See MCL 483.3(1)(a); Mich Admin Code, R 792.10447(1)(c). The PSC has set out a three-part test for determining whether to grant an application under Act 16. It must find that “(1) the applicant has demonstrated a public need for the proposed pipeline, (2) the proposed pipeline is designed and routed in a reasonable manner, and (3) 10 the construction of the pipeline will meet or exceed current safety and engineering standards.” In re Application of Enbridge Energy, Ltd Partnership, order of the Public Service Commission, entered January 31, 2013 (Case No. U-17020), p 5. See also In re Application of Wolverine Pipe Line Co, order of the Public Service Commission, entered July 23, 2002 (Case No. U-13225), pp 4-5. Any party in interest who is “dissatisfied with any order of the [PSC] fixing any rate or rates, fares, charges, classifications, joint rate or rates, or any order fixing any regulations, practices, or services, may . . . file an appeal as of right in the Court of Appeals.” MCL 462.26(1). The party appealing from such an order must “show by clear and satisfactory evidence that the order of the [PSC] complained of is unlawful or unreasonable.” MCL 462.26(8). See also In re MCI Telecom Complaint, 460 Mich 396, 427; 596 NW2d 164 (1999) (describing the deferential standards of review for certain PSC decisions). B. MEPA We next turn to the environmental protections guaranteed by our state Constitution and by statute. Article 4, § 52 of the Michigan Constitution of 1963 reads: The conservation and development of the natural resources of the state are hereby declared to be of paramount public concern in the interest of the health, safety and general welfare of the people. The legislature shall provide for the protection of the air, water and other natural resources of the state from pollution, impairment and destruction. Michigan’s Environmental Protection Act, 1970 PA 127, “mark[ed] the Legislature’s response to [that] constitutional commitment . . . .” Ray v Mason Co Drain Comm’r, 393 Mich 294, 304; 224 NW2d 883 (1975). MEPA “imposes a duty on individuals and 11 organizations both in the public and private sectors to prevent or minimize degradation of the environment which is caused or is likely to be caused by their activities.” Id. at 306. It “prohibits pollution, destruction, or impairment of the environment unless it can be shown that ‘there is no feasible and prudent alternative’ and that [a] defendant’s conduct ‘is consistent with the promotion of the public health, safety and welfare in light of the state’s paramount concern for the protection of its natural resources . . . .’ ” Id. (citation omitted; ellipsis in Ray). Put simply, MEPA bars environmentally destructive conduct unless it can be shown that the conduct is necessary and unavoidable. 5 MEPA “was the first legislation of its kind” and a “dramatic change” from prior practice in environmental protection, which vested environmental enforcement in administrative agencies without citizen participation. Id. at 304-305. Its provisions reflected “public dissatisfaction with the existing legal and regulatory regime.” Castrilli, Environmental Rights Statutes in the United States and Canada: Comparing the Michigan and Ontario Experiences, 9 Vill Env’t LJ 349, 361 (1998). The belief that administrative agencies were “too closely associated” with regulated interests and were unlikely to provide relief motivated the decision to vest enforcement in MEPA’s citizen intervention and lawsuit provisions. Id.; see also Ray, 393 Mich at 305 (“Not every public agency proved to be diligent and dedicated defenders of the environment.”). 5 MEPA differs significantly from its federal analogue, the National Environmental Policy Act (NEPA), 42 USC 4321 et seq. Unlike MEPA, “NEPA is a purely procedural statute” and “imposes no substantive environmental obligations or restrictions.” Seven Co Infrastructure Coalition v Eagle Co, Colorado, 605 US 168, 173; 145 S Ct 1497; 221 L Ed 2d 820 (2025). But, as will be discussed later in this opinion, notwithstanding their differences, MEPA and NEPA have some analogous provisions. 12  The Legislature did not attempt to promulgate a specific set of substantive environmental standards within MEPA, nor did it assign this task to an administrative agency. See id. at 306. Instead, the Legislature set “parameters” but “left to the courts the important task of giving substance to the standard by developing a common law of environmental quality.” Id. Although the statute contemplates that courts may adopt standards or procedures created by “the state or an instrumentality, agency, or political subdivision,” courts “may . . . [d]etermine the validity, applicability, and reasonableness” of any such standard, and “[i]f a court finds a standard to be deficient, direct the adoption of a standard approved and specified by the court.” MCL 324.1701(2)(a) and (b). See also Nemeth v Abonmarche Dev, Inc, 457 Mich 16, 30; 576 NW2d 641 (1998). Against this backdrop, MEPA provides several procedural pathways to enforce its requirements. Most notably, it creates a cause of action for private parties—and the attorney general—to seek declaratory and equitable relief in circuit court. See MCL 324.1701(1); see also MCL 324.1702 through MCL 324.1704. But, in addition to allowing “citizen suits,” 6 MEPA contemplates that agencies will also enforce its provisions. Section 1704 creates a mechanism for the circuit court to remit a MEPA action to an administrative agency for a decision in the first instance. MCL 324.1704(2) through (4). MEPA also 6 Lawsuits brought under MEPA by individuals or other entities have commonly been referred to as “citizen suits,” see, e.g., Sax & D