The U.S. Environmental Protection Agency on Friday said it intends to impose strict restrictions on the proposed Pebble mine to protect Bristol Bay's world-class salmon runs but is stopping short of blocking it outright.

EPA's work on Pebble already is the subject of a federal lawsuit, a watchdog agency review and much criticism from Republican political leaders and mine operators.

But Dennis McLerran, administrator of EPA's Seattle-based region 10, told reporters Friday that the action is necessary "to protect the world's greatest salmon fishery from what would most certainly be one of the largest open pit mine developments ever conceived of."

EPA isn't halting the mine even before operators apply for a permit. "This is not a preemptive veto," McLerran said.

The restrictions would prevent a mine of the size proposed by the Pebble Ltd. Partnership, which EPA says would create an open pit for copper and gold extraction nearly as deep as the Grand Canyon. But mine operators could scale back and develop a smaller, less destructive mine, EPA said.

Pebble, notified of the proposal just before it was published on the Federal Register, called it "outrageous." Environmental groups, tribal organizations, fishermen and jewelers all praised EPA.

"It's been a long time coming," said Luki Akelkok, chairman of Nunamta Aulukestai, an association of ten Bristol Bay tribes and Native village corporations.

Tribal groups petitioned the EPA in 2010 to block the mine through an obscure and rarely used section of the Clean Water Act. But instead of a quick veto, EPA began a three-year study of a mine's impacts on the Bristol Bay watershed.

Republican political leaders have pounced on EPA's work on Pebble as extreme "federal overreach."

The mine owners assert that EPA collaborated with mine opponents, a claim now under review by a federal watchdog.

In May, Pebble Partnership sued to stop EPA from shutting down the project, and the state has sided with Pebble in the lawsuit.

Just this week, a U.S. House committee approved a bill to keep EPA from blocking the mine.

At issue is a Corps of Engineers permit that mine operators would need in order to dredge and fill in wetlands.

EPA proposes barring a mine that:

  • Would destroy more than five miles of salmon streams or 19 miles of tributaries without salmon.
  • Fill in 1,100 or more acres of wetlands.
  • Reroute streams to more than 20 percent of the daily flow.

A less destructive mine would need to be evaluated closely, McLerran said.

Pebble officials say they are still reviewing the proposal.

"We are outraged, however, that the Agency decided to take this action when litigation on their underlying authority to do so is pending in Federal court in Alaska, and when their own Inspector General is currently in the process of reviewing the propriety of EPA's actions," Tom Collier, Pebble's chief executive, said in a written statement Friday.

Some scientists on a panel convened by EPA to review its study of the impacts of a big mine said that study should not be used as the basis for any action, Collier said.

But EPA says the scientists also praised the study as "very high quality" and that the agency has even more information in hand.

"We've got a very big and solid record here that goes above and beyond what the peer reviewers looked at," McLerran said.

EPA in February formally began the process of moving to protect the Bristol Bay watershed. The proposal of specific restrictions is the second step in a process that will extend for months.

Meanwhile, the Pebble Partnership has lost financial backing. In April, British and Australian mining company Rio Tinto pulled out of the partnership, giving away its stake. The move came after another large global mining corporation, Anglo American, departed in December. Northern Dynasty Minerals is now the sole owner of the Pebble prospect.

EPA will take public comments on the proposal until Sept. 19. A series of public meetings on the proposal will happen in Alaska in August.

After that process, EPA could pull back the proposal or send it to Washington, D.C., for approval.