The Michigan Supreme Court told state regulators to rethink a permit for a tunnel to carry an oil pipeline under the Great Lakes.

The court's decision makes the future of the 73-year-old pipeline less clear. The pipeline is owned by Enbridge and carries oil from Wisconsin to Ontario.

The part of the pipeline in question runs along the bottom of the Straits of Mackinac.

Enbridge wants to build a tunnel for the pipeline. But environmentalists and the governor want to move the pipeline away from the water. They say a spill would be very bad for the Great Lakes.

The Michigan Public Service Commission allowed the tunnel in 2023. But some tribes and environmental groups sued.

The court said regulators did not think about how the tunnel would affect the environment when they allowed it.

The court also said regulators did not compare alternatives to the pipeline fairly. They did not think about how the tunnel would affect fishing and boating.

Enbridge is delaying its plans for another pipeline project.

Opponents say this project has never been done before. It would turn a sacred site into a construction site for years.

An attorney said pumping oil through the Great Lakes is a bad idea. It would put the lakes at risk of an oil spill.

Enbridge is reviewing its options after the court decision. The company is disappointed in the delay.

Enbridge proposed the tunnel almost a decade ago. The company says the tunnel would reduce the risk of an oil spill. But environmentalists say it would cause damage to the environment.

The governor and other officials have been trying to shut down the pipeline since 2020.