All the hullabaloo over Hulu and YouTube has obscured one important trend in media: Documentary films are becoming increasingly common, and popular. You can't exactly blame Michael Moore, much as some would like to - Best Documentary Oscars have been given out since 1942. And early classics of the genre bear some surprises as well: 1925's epic Grass, about the annual migration of the Bakharti of Angora, Turkey, was directed by Merian Cooper, the same guy who gave us King Kong just 8 years later.

All of which is a long way of getting around to Rivers of a Lost Coast, a documentary that should be particularly close to our hearts here in the North Bay. The film (opening next week at the Rialto Lakeside, and playing now in special one-night screenings in Oregon) brings to life an era not that far in the past that is nonetheless like another world - a world where thousands of fly fishermen crowded the shallows of coastal waterways from Santa Cruz to Arcata, wading into waters so swarming with silvery salmon and steelhead that the fishermen were convinced their bounty could never, never be exhausted.

How wrong they were. Through little fault of their own, the once-abundant fisheries of the Klamath, Smith, Eel, Russian and San Lorenzo rivers collapsed in a relatively brief period of time. Now instead of millions, scant hundreds of wild anadromous fish (those which hatch in fresh water, reach maturity in the seas and return to reproduce in the gravel beds where they birthed) make the migration to natural spawning grounds. In 2008, as the film's closing titles tell us, state and federal fish agencies required the complete closure of recreational and commercial fishing on the coast, for the first time in over 150 years of regulation.

Rivers of a Lost Coast tells this story, from the glory days of the 1940s and 50s to the explosion of fly fishing's popularity in the 1960s, and the sudden evaporation of the fishing industry in the 1970s. The reasons for this collapse are but briefly explained: loggers decimated the hillsides and erosion poisoned the streams; so-called "100 year floods" changed the lay of the riverbeds in 1955 and 1964; dam-building by the Army Corps of Engineers choked off the spawning grounds from their progeny; and finally the drought of 1976 that dealt a deathblow to the North Coast fisheries. Even the wine industry of Sonoma and Mendocino doesn't escape blame, as the vineyards sucked up groundwater and reduced Russian River flows.

In the face of these catastrophic events, the obsessions of a relative handful of fly fishermen, whether or not they played by catch-and-release rules, seems irrelevant. Briefly touched upon are the mysterious fishing trawlers, long thought to be from Japan, that appeared off the California coast in the 70s and 80s and all but scooped up incoming salmon and steelhead before they could even reach the rivers.

Don't expect a how-to on fly fishing as a sport - if it's instruction you want, try a sports store. Instead, we meet the fishermen themselves, either in first-hand interviews or archival photos and footage with commentary. By far the most interesting is Bill Schaadt, who lived in a shack in Monte Rio practically buried in the found leavings of civilization: old bike parts, dish drainers, whatever he would pick up from the banks of the Russian River that no one else wanted.

He also apparently never purchased any fishing gear in his life: his entire kit was used, from rod to reel, line to lure, tattered and cobbled tackle that nonetheless served him to become the "guru of fishing," the best the era ever saw. "He had no family, no job, no new car. All he had was fishing," one contemporary recalls.

Schaadt's counterpart is Ted Lindner, his contemporary but the white knight to Schaad's black sheep - quiet, professional, resourceful. Their stories, like the others in Rivers of a Lost Coast, are told in an assemblage of photographs, home movies, magazine and newspaper clippings, and anecdotes. Justin Coupe and Palmer Taylor, the directors of the film, have done a great job of finding this material, and as research and rights are the core of the modern documentarian's challenge, they've done their job well.

Some of the footage is astounding: one clip shows what must be a 50-pound salmon torpedoing at surface level near the mouth of the Russian River, its surge creating a wake almost big enough to surf. It looks primal, unearthly, more like a danger from "Dune" than a prospect for dinner.

Despite the wealth of information and visual riches of the film, perhaps art direction has had too much say in the film's look. The design can and does overwhelm the story at times, with animated postcards, artificially degraded footage, gratuitous if not distracting special effects. Paired with the insistent, hypnotic, ultimately numbing music (from co-director Taylor), the film's aesthetics sometimes overwhelm its subject.

The memories and comments of the interviewees -- such as the artist and author Russell Chatham, Disney movie composer Mel Leven, or fisherman Tom Ugrin, who keeps his hands busy constantly making flies while being interviewed -- illustrate the story at least as well as the jazzed-up archival art. Their recollections of the amazing feeling of connection with the muscled vitality of these fish, or the sheer abundance of salmon who pulsed through the rivers, generate emotions we can only appreciate second-hand.

Ultimately, the deterioration of fly fishing in the northern counties is a tragic story; even though there is still catch-and-release fly-fishing in our rivers, it is almost entirely for hatchery fish. As narrator Tom Skerritt says at one point, "The elder generation eventually turned away from the coast. The sport was left to younger anglers, unburdened with the pain of casting to memories."

Still, the old-timers are never quite ready to give up. Smith River activist Ben Taylor weighs in toward the film's conclusion, "Maybe I'm a voice crying in the wilderness, and there's not much wilderness left, but I'll keep on crying as long as I'm around."