The U.S. Environmental Protection Agency is initiating a rarely used process under the Clean Water Act to identify appropriate options to protect the world’s largest sockeye salmon fishery in Bristol Bay, Alaska from impacts associated with a proposed Pebble Mine.

The Pebble Mine has the potential to be one of the largest open pit copper mines ever developed and could threaten a salmon resource rare in its quality and productivity, according to the EPA. During the EPA’s process, the U.S. Army Corps of Engineers cannot approve a permit for the mine.

This action, requested by EPA Administrator Gina McCarthy, reflects the unique nature of the Bristol Bay watershed as one of the world’s last prolific wild salmon resources and the threat posed by the Pebble deposit. It does not reflect an EPA policy change in mine permitting.

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“Extensive scientific study has given us ample reason to believe that the Pebble Mine would likely have significant and irreversible negative impacts on the Bristol Bay watershed and its abundant salmon fisheries,” said EPA Administrator Gina McCarthy. “It’s why EPA is taking this step forward in our effort to ensure protection for the world’s most productive salmon fishery from the risks it faces from what could be one of the largest open pit mines on earth. This process is not something the agency does very often, but Bristol Bay is an extraordinary and unique resource.”

The EPA is basing its action on available information, including data collected as a part of the agency’s Bristol Bay ecological risk assessment and mine plans submitted to the Securities and Exchange Commission.

This action follows the January 2014 release of EPA’s “Assessment of Potential Mining Impacts on Salmon Ecosystems of Bristol Bay, Alaska,” a study that documents the ecological resources of the region and the impacts to salmon and other fish from potential large-scale copper mining of the Pebble Deposit.

For information on the EPA Bristol Bay Assessment, go here