Michigan has filed a lawsuit asking for an Enbridge Inc. oil pipeline that runs under the Straits of Mackinac in the Great Lakes to be decommissioned, a statement from Michigan's attorney general said on Thursday.



The Line 5 oil pipeline ships 540,000 barrels per day of crude oil and propane and is a critical part of Enbridge's Mainline network, which delivers the bulk of Canadian crude exports to the United States.





The underwater portion of Line 5 has long been a bone of contention between Enbridge and the state of Michigan, which says a leak from the twin 66-year-old pipelines would cause catastrophic environmental damage to the Great Lakes.



In the lawsuit filed in the Ingham County Circuit Court, Michigan Attorney General Dana Nessel asked the court to find that Enbridge's continued operation of the Straits Pipelines under an easement granted in 1953 violates the public trust doctrine.



The lawsuit said the pipeline is a common law public nuisance and violates the Michigan Environmental Protection Act because it is likely to cause pollution impairment and destruction of water and other natural resources. It identified an anchor strike as the most significant risk to Line 5.



"The location of the pipelines ... combines great ecological sensitivity with exceptional vulnerability to anchor strikes," said Nessel in a statement.



"This situation with Line 5 differs from other bodies of water where pipelines exist because the currents in the Straits of Mackinac are complex, variable, and remarkably fast and strong."

The lawsuit seeks a court order to shut down and decommission the Straits pipelines as soon as possible after a reasonable notice period.



Nessel also filed a motion to dismiss an Enbridge lawsuit from earlier this month, that sought to enforce an agreement made with the previous governor of Michigan. That agreement would have allowed Enbridge to build a tunnel to house the underwater pipelines and continue to operate Line 5.



Calgary, Alberta-based Enbridge said it was disappointed that Michigan had not accepted its offer to advance talks on the Straits tunnel, and would need time to fully evaluate the Attorney General's filing.



"We believe the Straits tunnel is the best way to protect the community and the Great Lakes while safely meeting Michigan's energy needs," Enbridge spokesman Ryan Duffy said in a statement.