The U.S. Environmental Protection Agency said Friday that it is initiating a process under a rarely-used Clean Water Act to protect salmon fisheries in Bristol Bay, Alaska, from the proposed Pebble Mine.

Pebble Mine, located some 200 miles (320 km) southwest of Anchorage, has the potential to be one of the largest open-pit mines in the world due to the huge gold and copper deposits in the region.

About 3,000 tons of gold and 36 million tons of copper can be extracted within the next 30 years in the Bristol Bay area, AFP reported.

The proposed mine will come up at the headwaters of the Kvichak and Nushagak Rivers, two of the eight major rivers that feed Bristol Bay.

According to EPA, the mine will destroy native fish population.

Bristol Bay produces nearly half of world's wild sockeye salmon. The region's, "exceptional water quality in streams," is associated with the quality and quantity of fish found in the region, EPA said.

The region provides employment for over 14,000 people and is a sanctuary for 20 species of fish and over 190 species of birds.

"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 in a statement. "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."

The unprecedented move by the agency means that the promoters of the proposed Pebble Mine have to show that the mining wouldn't damage Bristol Bay ecosystem, AFP reported.

Pebble Partnership (PLP) was formed in 2007 as a 50:50 partnership between a subsidiary of Anglo American and Northern Dynasty Minerals, according to Department of Natural Resources in Alaska.

Anglo American pulled out from the venture last year, Reuters reported.

PLP said that the move by EPA is premature.

"We remain confident in our project and our position. We will continue to state our case with the EPA as we work through their process. The EPA's actions today are an unprecedented federal action and reflect a major overreach onto an asset of the State of Alaska. There is a prescribed, science based process for evaluating projects such as Pebble and the EPA has initiated a step that turns this process on its head," said Tom Collier, CEO of the Pebble Limited Partnership, in a statement issued Friday.