Gov. Gretchen Whitmer is fighting to shut down a crude oil pipeline in a battle that has long been waged in Michigan but is gaining attention nationally as environmental activists ramp up pressure on fossil fuel infrastructure across the country.

Whitmer, a Democrat, had ordered the 645-mile Line 5 pipeline operated by Canadian energy company Enbridge to shut down by May 12, citing risks that the pipeline could leak or spill oil any day. Enbridge’s Line 5, which carries up to 540,000 barrels per day of crude oil and natural gas liquids, runs under the Straits of Mackinac connecting Lake Michigan and Lake Superior. The Great Lakes is one of the world’s largest bodies of fresh water.