Updated

An Alaskan mine that may contain more than $500 billion in gold, copper and other minerals will never get dug if environmentalists get their way.

The proposed Pebble Mine, near the headwaters of Bristol Bay in southwest Alaska, could yield a staggering 107 million ounces of gold, 80 billion pounds of copper and 5.6 billion pounds of molybdenum, which is used to make steel alloys. Pebble Partnership, which wants to do the digging, is so confident of the bounty beneath the ground it has spent five years and $107 million monitoring the soil, water and air in order to assure the federal Environmental Protection Agency (EPA) it can mine without causing ecological damage.

"The quantity, grade and continuity of mineralization at Pebble ... demonstrate the project's potential to be one of the great metal producers of the 21st century," said Rod Thiessen, president and CEO of Northern Dynasty Minerals, which is working on the project with London-based Anglo American.

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But the lucrative mine is swimming upstream against a powerful environmental lobby that believes it would endanger the sockeye salmon habitat, wipe out entire streams, pollute other waterways and carve a maze of roads stretching hundreds of square miles. A draft watershed assessment by the U.S. Environmental Protection Agency released in May found that a possible failure of a dam holding waste from the project could spill into the fish habitat and poison salmon for decades to come. Pebble officials say the assessment is flawed because it is not based on any proposal from them, but on irrelevant mining scenarios. The company hasn't filed a formal proposal.

A public comment period on that assessment ended Monday and a peer review panel will examine the scientific and technical merit of the EPA assessment in Anchorage on Aug. 7-9. But some conservationists and commercial fishers told FoxNews.com they believe the EPA’s assessment is a significant blow to the proposed mine.

“If you read the watershed assessment, the conclusion that the EPA came to is that even without a catastrophic dam failure, there would be cumulative effects over time that would have an adverse effect on fish and other animals in the region,” said Lindsey Bloom, an organizer with Trout Unlimited and operator of a commercial fishing boat. “For us, if you look at the Exxon Valdez oil spill or the Deepwater Horizon spill in the Gulf, consumers just balk at the idea of potential pollution in their seafood.”

Bristol Bay — home to the largest sockeye salmon fishery in the world — contains all five species of North American Pacific salmon and provides at least 14,000 full- and part-time jobs annually, valued at roughly $480 million, according to the EPA. It also accounts for 46 percent of wild sockeye salmon worldwide and provides habitat to more than 190 bird species as well.

Bloom said Alaskans have long been “overwhelmingly” against the project over fears that a large-scale mine will fundamentally and irrevocably alter the region’s pristine landscape. Some natives also see the mine as one mega-industry stomping on local fisheries.

“I’m in favor of protecting existing jobs,” she said. “I see the mine as a potential job killer. It’s really big business versus big business. The fishing industry is the No. 1 job supplier in the state of Alaska. To me, that’s one business being threatened by another, and it’s not a 'save the baby whales' situation.”

Pebble officials say the project has support from Alaskans, and deny that it would imperil fish. Several local groups have weighed in either in favor of the project, or for giving the public more time to debate it.

"If the Pebble mine can be built and operated in a manner that protects the environment, it would provide the kind of economic development our communities desperately need," read a letter Nuna Resources, a local group which advocates sustainable development in the area, sent to EPA Administrator Lisa Jackson this week. "Jobs that could help people live comfortably here, even when gasoline costs $9 a gallon, a gallon of milk can cost more than $10, and electricity prices are five times the national average or more. Those jobs would also support our families and help revive our communities."

Pebble Partnership CEO John Shively calls the EPA document “rushed” and inadequate. Spokesman Mike Heatwole said the group is preparing to answer the “clearly flawed” report and questioned why the federal agency ignored calls for an extension of the public comment period. Pebble hasn't even formally applied for a permit, Heatwole said, and doesn't understand why the EPA jumped to block a mine he says will benefit the ailing state economy.

“Why the rush by the EPA?” Heatwole told FoxNews.com. “Why not listen to the state of Alaska?”

The mine has backing from some state officials. In June, state Attorney General Michael Geraghty wrote the EPA to complain of what he called an “unnecessary rush to judgment.” He sought to have the deadline for public comment extended to Nov. 20. Geraghty believes that if the EPA invokes the federal Clean Water Act in addressing the mining proposal, it could potentially “extinguish” the state’s mineral rights.

EPA officials, meanwhile, said that the agency has made no judgments about the use of its regulatory authority under the Clean Water Act and the draft study in no way prejudges future consideration of proposed mining activities. Officials told FoxNews.com the agency has worked with the fishing industry and other "important stakeholders" to make sure all voices are heard. But they said the project has to get an up or down vote at some point.

“In order to ensure that the final assessment is released in a timely fashion, it is imperative that this process move forward on schedule,” the agency said in a statement.

Meanwhile, in September, Sen. Maria Cantwell, D-Wash., became the first senator to call on the EPA to use its Clean Water Act authority to block any large development project if science determined it have "unacceptable adverse impacts" on water quality and the fish that depend on it.

Sen. Lisa Murkowski, R-Alaska, believes the EPA's draft assessment may have been the first in that process and has questioned why the EPA did not allow a longer public comment period.

“This is the first time the EPA has conducted a preemptive assessment of an entire watershed without even having a specific project description to evaluate," Murkowski said in a statement to FoxNews.com. "Given the potential impact on the state’s economy, I’m disappointed the EPA did not allow Alaskans, many of whom are busy 24-hours a day during our short summers with commercial and subsistence fishing, more than 60 days to comment.”

The Associated Press contributed to this report.