An environmental group is threatening to sue the federal government over a Great Lakes oil pipeline.
The National Wildlife Federation notified the Pipeline and Hazardous Materials Safety Administration on Monday.
The group is targeting Enbridge Energy's Line 5, which runs from Superior, Wisconsin, to Sarnia, Ontario.
A nearly 5-mile-long section reaches beneath the Straits of Mackinac, the link between Lakes Huron and Michigan.
Enbridge says the underwater section has never leaked and remains safe.
Environmentalists want it removed.
The wildlife federation says the federal agency had no authority to approve oil transport through pipelines extending through the straits or other navigable waterways in Michigan.
t says the agency failed to assess the potential effects on fish and animals.
The agency did not respond immediately to a request for comment.