Those fighting to save Bristol Bay from the Pebble Mine operation moved once step closer to victory last week – but mine supporters have vowed to go down swinging.

Opponents of the mine that threatens the priceless fisheries in Bristol Bay, Alaska – and the self-sustaining industries they support – were thrilled by the surprise EPA announcement it will invoke rarely used authority under the Clean Water Act to preemptively limit or stop the mine before the permit is filed because of its potential harmful impacts.

The action came just weeks after the EPA released a study showing the mine would be devastating to fisheries, the industries they support and the native cultures that depend on them.

EPA Administrator Gina McCarthy referenced that report in this latest announcement, saying the study has provided “ample reason to believe that the Pebble Mine would likely have significant and irreversible negative impacts” on the watershed and its salmon.

The agency will be using Sector 404(c) of the CWA, which gives the administrator to ability to act preemptively. It has been used only 29 times. In 13 of those cases the EPA limited or stopped the proposed development.

McCarthy said the action was being taken “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.”

Mine developers have sworn to oppose that action, and they’re backed by Governor Sean Parnell, U.S. Sen. Lisa Murkowski, and U.S. Rep. Don Young, all Republicans.

Opponents of the mine are relying on national environmental regulations and policies that protect renewable public resources that oftentimes are one-of-a-kind. Development supporters, meanwhile, claim the economic boost can be accomplished without permanent harm, and call the use of federal regulations an overreach into state affairs – even though the location is national property.

The Anchorage Daily News provides an excellent, up-to-date summary of the issues.