The U.S. Environmental Protection Agency (EPA) released its final assessment of the impact of large-scale mining in Alaska’s Bristol Bay region on Jan. 15 and the findings are similar to the agencies draft report that found large-scale mining could adversely affect the world’s largest sockeye salmon fishery.

Like the draft report before it, the final assessment is not an in-depth assessment of a specific mine, but a study of the possible impacts of what the EPA called reasonably foreseeable mining activities in the region. The agency said it drew on a preliminary plan published by Northern Dynasty Minerals and consulted with mining experts on reasonable scenarios, The Associated Press reported.

Northern Dynasty Minerals is working to build the Pebble Mine in the region, potentially one of the largest openpit mines in the world, with the potential of producing 80.6 billion lbs of copper, 107.4 million oz of gold and 5.6 billion lbs. of molybdenum over the life of the mine.

"Publication of the final watershed assessment is really the final chapter in a very sad story," said Northern Dynasty president and chief executive officer Ron Thiessen. "We believe EPA set out to do a flawed analysis of the Pebble Project, and they certainly succeeded with both their first and second drafts of the Bristol Bay Watershed Assessment (BBWA). We have every expectation that the final report released today is more of the same."

Thiessen said the final BBWA report does not include any recommendations or regulatory actions that will affect future development of the Pebble Project.

"We look forward to defining a proposed development plan for Pebble and to having it reviewed by federal and state regulatory agencies under the National Environmental Policy Act (NEPA) in the months and years ahead," Thiessen said. "We have every expectation that the Environmental Impact Statement (EIS) process required by NEPA, to be administered by the US Army Corps of Engineers, will ultimately provide a much more rigorous, fair and transparent review of the science surrounding this important project."

In its report the EPA concluded that, depending on the size of the mine, up to 151 km (94 miles) of streams would be destroyed in the mere build-out of the project, including losses of between 8 and 35 km (5 and 22 miles) of streams known to provide salmon spawning and rearing habitat.

"Our report concludes that large-scale mining poses risks to salmon and the tribal communities that have depended on them for thousands of years. The assessment is a technical resource for governments, tribes and the public as we consider how to address the challenges of large-scale mining and ecological protection in the Bristol Bay watershed," EPA regional administrator Dennis McLerran said in a statement.

EPA initiated the review process in response to a request in 2010 from tribes and others in the region concerned about the impact of the proposed Pebble Mine on Bristol Bay fisheries. 

Supporters of the EPA process hoped it would lead the agency to block or limit the project, while opponents saw it as an example of government overreach and feared it would lead to a pre-emptive veto.

EPA has said its goal with the watershed assessment is to get the science right. In the report, EPA said the assessment will inform possible future government actions.