Pigeonroost Branch is home to crayfish, mayfly and fish. The stream flows through the Spruce Valley in northeastern Logan County.
Hobet Mining Inc. wants to fill more than a mile of the creek with millions of tons of rock and earth from what would be the largest strip mine in state history.
The U.S. Department of the Interior has concluded the proposal would violate federal and state water-quality rules, according to a new report issued in late July.
In its first official action in the growing controversy over mountaintop removal, Interior's Fish and Wildlife Service urged regulators to conduct further studies of the proposed mine's potential effects.
"We do not believe that the state has adequately assessed the effects of this project on waters of the United States," wrote David Densmore, supervisor of the Fish and Wildlife Service field office in State College, Pa.
Hobet, an Arch Coal Inc. subsidiary, wants a permit from the state Division of Environmental Protection to expand its Dal-Tex complex near Blair.
The mine expansion would cover roughly five square miles along Pigeonroost Branch. The operation would produce 80 million tons of coal - about $2 billion worth - over a 15-year period.
The U.S. Environmental Protection Agency has temporarily blocked DEP from issuing a water pollution permit for the mine. EPA wants more information about the mine's potential environmental impacts.
EPA's objection to the permit was based in part on an analysis conducted by the Fish and Wildlife Service.
That report was made public last week when it was attached to motions filed by environmental groups in a federal court lawsuit which challenges mountaintop removal permitting.