LANSING – Unless Enbridge returns to the negotiating table, it appears inevitable that Attorney General Dana Nessel will move to shut down the Enbridge Line 5 oil and gas pipeline through the Straits of Mackinac, Gov. Gretchen Whitmer said Wednesday.

Whitmer, speaking to the editorial board of the Lansing State Journal, said she entered negotiations with Enbridge to agree on a firm date "when we could know that the line was going to be out of the water."

However, "Enbridge could not or would not have that conversation, and I found out through the media that they were suing me to enforce the agreement that they had with the (former Gov. Rick) Snyder administration," Whitmer said.

That agreement, backed by legislation rushed through the Legislature during the December lame-duck session, said Enbridge would pay to dig a tunnel into bedrock beneath the straits. A replacement pipeline would be encased inside the tunnel, protecting it from threats such as anchor strikes and preventing the mixing of oil and Great Lakes water if a leak should occur.

The agreement hasn't quieted opponents of the line, who say the Great Lakes remain at too much risk while the line continues to operate as the proposed tunnel is built.

More:Enbridge seeks court ruling on Great Lakes oil pipeline deal

More:Michigan AG Dana Nessel will give Line 5 negotiations a few more weeks

Whitmer said Nessel will be filing a response to the Enbridge lawsuit, which was filed in the Michigan Court of Claims on June 6. When she files that response, Nessel may be filing a countersuit setting out "another theory or another cause of action," Whitmer said.

"As court plays out, I think there's always the possibility that Enbridge could come back to the table," and agree on a date for getting the line out of the water," she said. "But short of that, I have a hard time seeing how the attorney general doesn't press on with her theory of lawsuit."

Ryan Duffy, a spokesman for Enbridge, said Wednesday that despite the lawsuit, "we are open to resume discussions with the governor at any time."

As for a fixed date to get the line out of the water, "we can begin tunnel construction by 2021 and be in service by 2024," he said.

That's more aggressive than earlier estimates that said it could take seven to 10 years to complete the tunnel.

Duffy said that both Enbridge and Whitmer agree on ensuring the safety of the Great Lakes.

"We’re committed to moving forward with the Line 5 tunnel project, which would invest $500 million into the state to ensure security of energy supply and further protect the natural resources that we all treasure," he said.

Nessel will file her response to the Enbridge lawsuit on June 27, a spokeswoman said.

The idea of Nessel moving to revoke the easement the state granted Enbridge to cross the Straits of Mackinac has received extensive discussion, but Nessel, and now Whitmer, have alluded to other legal theories that could be used to get the pipeline out of the straits.

Environmental attorneys have said that notwithstanding the agreement Enbridge struck with the Snyder administration, Whitmer and Enbridge could require the company to make an application under the Great Lakes Submerged Lands Act before starting a tunnel dig. If required, that application would be subject to approval by the Whitmer administration.

Proponents of the tunnel plan say it's the best way of getting the pipeline out of the water while ensuring an uninterrupted and affordable supply of propane to Michigan's Upper Peninsula and oil to the Marathon refinery in Detroit and other U.S. customers.

Opponents say Line 5 mostly moves Canadian oil to Canadian customers and other alternatives can be found to serve Michigan customers. Michigan remains at risk of a catastrophic spill while the tunnel is being dug, they say.

Snyder, a Republican who left office Jan. 1 because of term limits, struck a deal for Enbridge to build the tunnel shortly before he left office and pushed enabling legislation through the GOP-controlled Legislature.

Nessel issued an opinion in March that said the tunnel legislation violates the Michigan constitution, because it did not have a single purpose, described in its title, as the constitution requires.

In its lawsuit, Enbridge said "the state now refuses to honor the promises made in the December 2018 agreements."

Contact Paul Egan: 517-372-8660 or pegan@freepress.com. Follow him on Twitter @paulegan4. Read more on Michigan politics and sign up for our elections newsletter.