"DELTA TOWNSHIP, Mich. — Operators of twin oil pipelines beneath the swirling waterway where Lakes Huron and Michigan converge insisted Monday they remain structurally sound even though an outer layer of protective covering has worn away in some places, while skeptics said the deterioration is further evidence the lines should be shut down.

Officials with Enbridge Inc. said the exterior material is not essential to the pipes' integrity and there is no reason for concern about its absence in spots along the lines extending nearly 5 miles along the bottomlands of the Straits of Mackinac.

'If there was ever a time when we weren't 100 percent confident in its fitness, we wouldn't be operating the pipeline,' Brad Shamla, the Canadian company's vice president of U.S. operations for liquid pipelines, told reporters before a meeting of the Michigan Pipeline Safety Advisory Board."

David Eggert and John Flesher report for the Associated Press March 13, 2017. [2]