The U.S. Army Corps of Engineers on August 12 issued a final permit for a tunnel project beneath the Straits of Mackinac, authorizing Canadian energy company Enbridge to relocate a segment of its Line 5 pipeline under Lake Michigan and Lake Huron. The permit is the only federal authorization required for the project, which would house a 4-mile section of Line 5 in a tunnel bored 60 to 250 feet below the lakebed.
The Line 5 pipeline, constructed in 1953, currently spans the Straits of Mackinac with two exposed pipes. Enbridge states the tunnel would eliminate risks such as anchor strikes, structural damage, and wear to the pipeline’s protective coating. The company applied for the Army Corps permit in 2020, and the project was fast-tracked in April 2025 as part of a broader push to expand U.S. oil and gas infrastructure under the Trump administration.
State and legal challenges remain. Michigan’s Supreme Court recently ordered the state’s Public Service Commission to redo its analysis of the project, reversing a December 2023 approval. Additionally, the Michigan Department of Environment, Great Lakes and Energy—led by Gov. Gretchen Whitmer—reissued a wetlands and bottomlands permit in July 2025 after a 16-month review, despite Whitmer’s prior efforts to shut down Line 5 over spill risks.
Federal and state rationales
The Army Corps stated the permit complies with all federal laws and regulations following its environmental review. Adam Telle, Assistant Secretary of the Army for Civil Works, framed the approval as part of the administration’s "Building Infrastructure, Not Paperwork" initiative, emphasizing regulatory efficiency and energy security. The Army Corps noted the project aligns with Congressionally-mandated permitting responsibilities.
Michigan’s environmental agency justified its permit reissuance by citing additional wetlands-survey data submitted by Enbridge, which it said addressed prior concerns. The agency’s decision followed Enbridge’s voluntary expiration of its 2021 permit to reapply under updated conditions.
Opposition and concerns
Environmental groups and tribal nations have filed legal challenges to block the tunnel and shut down Line 5, citing risks of oil spills into the Great Lakes. Critics argue the tunnel project undercuts Whitmer’s prior shutdown efforts and fails to address long-term environmental threats. Historical incidents, including anchor strikes and coating damage, have raised alarms about the pipeline’s integrity.
The tunnel would run from the south shore of the Straits of Mackinac to the northern shore, with construction expected to begin only after resolution of ongoing litigation and state-level reviews. Enbridge maintains the project would nearly eliminate the risk of a pipeline incident by removing the pipeline from direct contact with lakebed activities.