The construction of Line 5 was completed in 1953. In 2013, the line's capacity was increased by per day, from . The upgrade involved US$100 million in improvements to pumping stations, but with no upgrades to the actual pipes. In 2018, a tugboat anchor hit the pipeline, causing a fluid leak and minor damage to the pipe. Also in 2018,
Enbridge and the
State of Michigan agreed to build a tunnel beneath the
Straits of Mackinac that will contain the pipeline. Line 5 in the Straits consists of two 20-inch pipelines, an east leg and a west leg, running parallel to each other for the 4.5 miles across the lakebed. On June 18, 2020, a screw anchor support on the east leg was found to have shifted from its original position. The shift was caused by Enbridge's seasonal maintenance work, which affected the anchor support and not the pipeline itself. On June 20, 2020, Enbridge reported that a June 19 remote-operated vehicle inspection of the west leg of Line 5 in the Straits had detected no issues or damage to the anchor structures or pipeline. Operations resumed on that line on the same day. The east leg was to remain shut down. The federal regulator,
Pipeline and Hazardous Materials Safety Administration raised no objections to the plan. Enbridge CEO Al Monaco responded to Michigan Governor
Gretchen Whitmer to confirm that Enbridge was committed to sharing what is learned about the incident with the screw anchor assembly on the east leg with PHMSA and the State of Michigan.
Mackinac Straits Corridor Authority (MSCA) agreement about tunnel On December 19, 2018, the
Michigan Department of Natural Resources announced that the Mackinac Straits Corridor Authority (MSCA), in correspondence with outgoing Governor
Rick Snyder, had approved a plan to build a multi-purpose tunnel that would house multiple utility lines, to remove the old Enbridge Line 5 and to construct a new line. The MSCA approved the transfer of a property right, allowing Enbridge to construct the new tunnel in the bedrock beneath the
Straits of Mackinac. The project has faced fierce opposition from environmentalists and several tribal authorities. were then shipping 540,000 barrels of oil and propane per day. A
Reuters news report defined Line 5 as "a critical part of Enbridge's Mainline network, which delivers the bulk of Canadian crude exports to the United States". The basis of the suit is the claim that the pipeline is a public nuisance and violates the Michigan Environmental Protection Act since it may become a major source of pollution. The news report added that "it is unclear if Line 5 could operate without the Straits segment". Attorney General
Dana Nessel commented: "We cannot prevent accidental or emergency anchor deployments in one of the busiest shipping channels in the Great Lakes. And it only takes one such incident to cause an environmental and economic catastrophe. That is a risk no one should be willing to take". Michigan Senate Republicans expressed concern about the potential shutdown of the pipeline, which they said could create other problems: "the loss of thousands of construction jobs expected from the tunnel construction, an increase in costs at Detroit and Toledo refineries and the loss of a significant mode of propane transportation in Michigan. It is estimated that replacing the propane lost by closing the line would require an additional 30,000 truckloads and 9,600 rail cars annually". In June 2020, the
U.S. Sixth Circuit Court of Appeals ruled the emergency response for the pipeline was adequate to protect wildlife in the Straits of Mackinac and the
Michigan Court of Appeals sided with its ruling. Enbridge has stated that the pipeline is in good condition even though the outer coating has worn away in some places and steel braces are placed at places hit by erosion. It plans the construction of a
utility tunnel in the bedrock under the Straits of Mackinac-the connector of
Lake Michigan and
Lake Huron, to house the Line 5 pipeline and to replace its six-kilometer underwater segment. Enbridge intends to begin work on the tunnel once it received all the necessary permits and expected to complete construction by 2024. In 2019, the
Bad River Band of Lake Superior Chippewa filed a lawsuit against Enbridge. Enbridge was ordered to find an alternative route or shut the pipeline down by June 2026. The pipeline supplies fuel to much of Ontario and Quebec. ==Controversies==