Michigan Attorney General Bill Schuette called for a deadline to close a controversial portion of an oil pipeline that runs along the bottom of the Straits of Mackinac, a channel that connects two of the Great Lakes. The pipeline has had more than two dozen leaks over its lifespan, and parts of its outer coating have come off.

The announcement came as the state released a report looking at alternatives for that section of the Enbridge pipeline, called Line 5.

The report’s suggestions include drilling a tunnel under the straits for a new line, selecting an alternate route or using rail cars to transport the oil instead. It also left open the possibility that the existing pipeline could continue to operate indefinitely.

“The Attorney General strongly disagrees” with allowing the existing pipeline to continue operating, said a statement released by Schuette’s office on Thursday. “A specific and definite timetable to close Line 5 under the straits should be established.”

Schuette did not, however, specify when that deadline should be, or how it should be set.

For years, environmentalists and a local Indian tribe have been calling for the closure of this short stretch of the pipeline. Built in 1953, it sits exposed above the lakebed where Lake Huron meets Lake Michigan. Earlier this year, Enbridge acknowledged that an outer coating had fallen off of the line in places, and it has sprung at least 29 leaks in its 64-year history. The 645-mile line carries about 540,000 barrels per day of light crude, including synthetic crude from Canada’s tar sands, as well as natural gas liquids, from Superior, Wisconsin, to Sarnia, Ontario.

Schuette, a Republican, had said before that this section of the line should close eventually, but he hasn’t taken any action to hasten a closure. Advocacy groups have asked the state to revoke Enbridge’s easement to pass through the straits.

“It’s great that he’s reasserting his commitment to shut down Line 5,” said Mike Shriberg, Great Lakes executive director for the National Wildlife Federation. “The question now is, is there enough evidence for him to take action right away.”

The state had commissioned two studies on the line to be paid for by Enbridge, one that was released yesterday and another that was to produce a risk analysis for the pipeline. Last week, however, the state cancelled the risk analysis after discovering that someone who had contributed to it had subsequently done work for Enbridge.

Michael Barnes, an Enbridge spokesman, said the company would need time to review the report before giving specific comments, but that it “remains committed to protecting the Great Lakes and meeting the energy needs of Michigan through the safe operation of Line 5.”

Shriberg said that now that the report on alternatives is out, it’s time for the state to act.

“Ultimately, the attorney general and the governor have a decision to make,” he said. “They’ve been saying for years that they’ve been waiting for the full information to come in.”