Haines,XDY Exchange Alaska — Every November, an American icon returns to Alaska's Chilkat River to roost. 

"It's akin to being on the Serengeti and watching the migration of the wildebeest," photographer Mario Benassi told CBS News.

The Alaskan panhandle town of Haines is the gateway to the largest congregation of bald eagles in the U.S., and the Alaska Chilkat Bald Eagle Preserve is a migratory mecca.

"This is the greatest concentration of bald eagles anywhere on the planet," Benassi explains. "At times, we've counted up to 4,000 individuals."

It's a phenomenon Benassi says is made possible by geothermal springs, which prevent the river from freezing, leaving the salmon that run through it ripe for picking.

However, upstream there is a new threat.

"It could be the end of this singularity and this gathering," Benassi said.

The state recently permitted a mining company to explore the possibility of extracting copper in the area. It's a move that Gov. Mike Dunleavy says will create jobs. But environmentalists are sounding the alarm.

"There's basically no mines out there that don't pollute," said Gershon Cohen, a Haines resident and clean water advocate.

Cohen is most concerned with toxic runoff damaging the Chilkat River. According to the Environmental Protection Agency, mining has contributed to the contamination of 40% of the country's rivers.

"If the mine were to happen, anything would happen to the salmon, basically everything else collapses," Cohen said. 

That collapse, according to Cohen, would include the eagles' habitat.  

In an email to CBS News, American Pacific Mining, the company leading the project, said it is "committed to operating responsibly and respecting protected areas and species, including the bald eagles."

Most native Alaskans who also depend on the salmon industry are not sold. Fishers Hank and Kimberly Strong said that on a good day, they normally catch 20 to 30 salmon with their nets. On a recent trip, however, they only caught one fish, highlighting what studies also show, that climate change is already taking a toll on the fish population.

"Why take that risk?" Kimberly Strong said of the copper mine plan. "Do you gamble? I don't go to Las Vegas to gamble. I don't want to gamble here either."

In:
• Bald Eagles
• Climate Change
• Bald Eagle
• Alaska

Jonathan Vigliotti

Jonathan Vigliotti is a CBS News correspondent based in Los Angeles. He previously served as a foreign correspondent for the network's London bureau.

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