We Coloradans like to boast about big trout, but Mongolians put our fish tales to shame: Their taimen weigh as much as 50 pounds and can exceed six feet in length. They’re what trout might look like in Alice’s Wonderland. But the realities of mining and other human impacts are decimating this species, which ranks as the biggest member of the trout family.

A coalition of American fishing guides, conservationists, and researchers is trying to save these fantastical creatures from extinction. Their efforts are depicted in a new film—One Path: The Race to Save Mongolia’s Giant Salmonids—which will premier at the Denver Film Festival (DFF) this weekend.

The film follows a fishing expedition led by Mongolia River Outfitters, a guide service founded by Mark Johnstad back in the early 1990s. Even then, Johnstad recognized that no outsider could support taimen populations as effectively as local Mongolians could, so he approached the communities’ best taimen hunters and offered them jobs as fly-fishing guides. That turned some of the species’ biggest predators into protectors, and sparked locals’ interest in growing an economy of tourism around these amazing fish.

But Johnstad saw that saving taimen would require more than a handful of fishing guides. Mining, overgrazing, and other forms of human development have pushed taimen out of their historic range, which once included Russia, China, Japan and Korea. Now, only western Mongolia still maintains healthy taimen populations, and even those numbers have declined by at least 50 percent since 1985.

One Path documents how, during one fishing trip last fall, Johnstad broadened his campaign by staging a taimen festival on the banks of the Delgermörön River. He organized games centered around taimen and their conservation, but he also offered something that rural Mongolians really need and care about: health care. A dentist from Oregon and a pediatric cardiologist from Ohio worked a daylong clinic where they filled cavities and issued check-ups.

“I have to believe that those families are now more invested in taimen conservation,” says Ross Purnell, one of the fly-fishers on the trip and One Path’s central character (Purnell is also Editor-in-Chief of Fly Fisherman magazine). In a sense, the festival employed experiential marketing: By linking taimen to a positive, feel-good event for local Mongolians, the anglers hoped to raise popular support for the beleaguered fish.“This is their river, this is their river valley, and if they don’t care about the taimen, the taimen are not going to survive,” Purnell says.

One Path also shows how Purnell and the trip’s other anglers collected data for the University of Nevada at Reno, where researchers are studying the taimen’s migration and genetics. Anglers tagged each specimen they caught with a GPS tracker and snipped a swatch of its fin to provide scientists with the fish’s DNA. All that gives One Path more depth than your typical fish film—though it’s still got enough big-fish action to satisfy audiences who just love to watch people catch trophies (and that demographic includes me).

You can ogle the big’uns at the Paramount Theater on Sunday, November 4, when One Path premieres as part of the 41st annual DFF (tickets are $30). Proceeds from ticket sales and a silent auction benefit The Taimen Fund, and live music and beer round out the party (which also celebrates the 50th anniversary of Fly Fisherman magazine).

For even more taimen talk, hit DFF’s panel discussion the day before the film’s premiere: On November 3 at McNichols Civic Center, Purnell will join several taimen guides (including two native Mongolians) as well as Charlie Conn of The Taimen Fund and Lanie Galland of the University of Nevada in a conversation about taimen conservation.

It’s a fish story worth tuning in for.

Did You Know?

As the official sister city to Mongolia’s capital, Ulaanbaatar, Denver has the largest population of Mongolian immigrants living in the U.S.