(CNN) — It is the question that pits neighbor against neighbor, tribe against tribe, and Republican against Republican.

Should America risk the last great salmon run on Earth to dig what could be the richest mine on the planet?

Should Alaska gamble the red gold that swims into their nets and feeds tens of millions to chase the yellow gold and copper craved by world markets?

As salmon make their journeys to spawn, they provide nutrients that sustain a variety of Alaskan wildlife, including brown bears. Bill Weir/CNN

At the center of this question is the proposed Pebble Mine, a massive mineral deposit worth between $300 billion and $500 billion being pursued by the Canadian mining company Northern Dynasty and intended to be built in southwestern Alaska.

It all began in the 1980s, when a helicopter survey team noticed a strange red spot on a windswept stretch of land north of the state's Bristol Bay.

Part of the intricate watershed that connects Bristol Bay with the site of the proposed Pebble Mine. Bill Weir/CNN

In 2001, Northern Dynasty purchased the property and discovered a mother lode near Lake Iliamna. Officials estimate that beneath that red spot lies 100 million ounces of gold and 80 billion pounds of copper spread deep and wide across this mass of breathtaking land.

But to get it all, Northern Dynasty would need massive amounts of explosives and machinery to turn this pristine wetland into one of the biggest man-made holes in the world. Along with new roads, ports and power lines, the process would also create lakes of toxic wastewater, tainted with sulfuric acid.

A fishing fleet in Kodiak, Alaska, waits for the salmon run to arrive. The last few seasons, these boats helped bring in a record catch of over 50 million sockeye and king salmon. Bill Weir/CNN

That is exactly what worries the fishing communities downstream.

"If pollution gets into that water supply," says Dan Schindler, head of the Alaska Salmon Program, "it's going to be nearly impossible to contain."

He is the head ecologist for the University of Washington and has spent his life studying how tens of millions of king and sockeye salmon surge through Bristol Bay each summer, on their way to spawn in the exact lake or stream of their birth.

Alaska's fisheries supply nearly half of the world's supply of sockeye salmon. Bill Weir/CNN

As these squirming schools defy gravity by surging upstream, they inject ocean nutrients into the land and feed every form of life, from bears to eagles to humans. With a constitutional mandate to protect the run, Alaska limits the catch, but still manages to net nearly half of the world's supply of sockeye each July.

More than two billion salmon have been caught in Bristol Bay since records began, and fish are the lifeblood of local industry.

In 2014, after three years of peer-reviewed study, the Obama-era Environmental Protection Agency determined that the fishery was too valuable to risk and too complex to mine. With a damning report, it invoked a rarely-used provision of the Clean Water Act to protect Bristol Bay.

As mining partners bailed out and Northern Dynasty's stock plummeted, the company spent millions suing the EPA. The "Stop Pebble Mine" stickers faded around Dillingham and Naknek and it appeared that the fishermen and environmentalists had won.

As a Republican president of the Alaska Senate, Rick Halford approved most mining proposals, but is a fierce opponent of Pebble Mine. "It doesn't mean that we don't need minerals. It doesn't mean that we don't need mining," he said. "But this is not the place." Bill Weir/CNN

But then Donald Trump became President.

And in May, hours after meeting with the CEO of the Pebble Partnership, the new head of the EPA, Scott Pruitt, withdrew his agency's plan to protect Bristol Bay. Since they've already invested $700 million and no longer face federal opposition to the project, Northern Dynasty can now proceed with permit applications.

Pebble Partnership says the mine would be "in harmony with the environment" and create jobs.

"The minerals that they're talking about are the kinds of minerals that people use every day, in your cameras, in your cell phones, in Fort Knox," fisherman Gaylord Lee Clark told me as he piloted his salmon boat through Bristol Bay. "You are already exacerbating the situation by demanding the minerals that ... you positively must have for your life, (and) at the same time you're trying to maintain a salmon run so that you can eat well. What do we do?"