Michigan authorities said Canadian pipeline company Enbridge offered assurances two oil pipelines running under the Mackinac Straits are secured.

Line 5 of the Lakehead pipeline system splits into two 20-inch pipelines that carry the heavier grade of crude oil beneath the straits separating the Upper and Lower Michigan Peninsulas. They were installed in 1953.

Since an oil spill from Line 6b of the system in 2010, Enbridge has faced scrutiny about the integrity of the pipeline system. That spill was one of the worst onshore incidents of its kind in U.S. history.

The Michigan Petroleum Pipeline Task Force said it met with Enbridge officials to discuss Line 5 integrity.

A presentation delivered to the task force says pipeline sections are nearly an inch thick and are designed to safely deliver oil or natural gas "for decades."

"Company officials also asserted that testing and inspection of the pipelines show they maintain nearly 99 percent of their original integrity," the task force said.

Liz Kirkwood, executive director of state advocacy group Flow for Water, said Monday her concern was a pipeline designed to carry hundreds of thousands of barrels of oil per day was running through 20 percent of the world's fresh water. The task force, she said, is inadequate.