WILDERNESS -- Environmentalists are challenging U.S. Forest Service approval of a $500 million copper and silver mine in northwest Montana, citing concerns from state officials that it could drain surrounding waterways and potentially harm a species of trout protected under federal law.

The lawsuit filed Friday in U.S. District Court in Missoula challenges the Montanore Mine south of Libby near the Idaho border, the Associated Press reports. Sponsor Mines Management Inc. of Spokane has been seeking a mining permit since 2004.

But three groups said in Friday’s lawsuit that the government’s authorization for Montanore ignored studies of the mine’s environmental effects. Those government-sponsored studies concluded the mine potentially could drain groundwater supplies that feed into creeks and a river in the pristine area, an effect that could linger for centuries.

Earthworks, the Clark Fork Coalition and Save Our Cabinets said the water depletions would cause severe damage to the habitat of federally-protected bull trout.

“It’s simply not smart to treat wilderness waterways this way,” said Karen Knudsen with the Clark Fork Coalition. “There are laws in place that require the Forest Service to make sure any action complies with state water laws. The Montana Department of Environmental Quality thinks the project that’s proposed doesn’t.”

Representatives of the Forest Service and Mines Management did not immediately respond to requests for comment.

During its decades of operations, the mine would disturb more than 1,500 acres and remove up to 120 million tons of ore.

In approving the project in February, Kootenai National Forest Supervisor Christopher Savage said the agency’s action was contingent on Mines Management obtaining permits from state regulators and the U.S. Army Corps of Engineers. But so far Montana regulators have granted only conditional approval, pending more evidence from the mine’s backers that it won’t drain overlying creeks.

The state’s action on Montanore has drawn a backlash from Republicans hoping to unseat Democratic Gov. Steve Bullock. They’ve accused the administration of stalling on a project that would employ about 500 people during construction and about 350 people during mining.