MONTREAL -- The top-grossing English-Canadian film this month is a documentary about the impact of the giant Three Gorges Dam project in China. In fact, the description English-Canadian is a bit of a misnomer here, because the dialogue in "Up the Yangtze" is in both English and Mandarin, and Montreal-based writer-director Yung Chang is a Canadian of Chinese descent.

Chang has made an intimate, personal film that mostly focuses on one Chinese teen girl, Yu Shui, and her poor farming family. She signs on to work on a cruise ship that travels the Yangtze River, giving Western tourists one last glimpse of a landscape that is going to be forever changed once the dam is fully finished. Chang gently underlines cultural clashes on the cruise ship but avoids any direct political pamphleteering.

In spite of the way-off-the-beaten-track subject, the film, co-produced by Montreal outfit EyeSteelFilm and the National Film Board of Canada, has become one of the more notable Canuck domestic hits in recent memory. In the first week of April, the film was the No. 2 domestic performer at the box office and the top non-French homegrown pic. (French-language films tend to do much better at the box office than their English counterparts.)

"Up the Yangtze" has so far rung up C$475,000 ($474,000) at the cash register in Canada since its release in early February on a single screen in Toronto. Even now, it is playing on only eight screens across the country. The success is all the more notable given that EyeSteelFilm has released the film itself, with help from small Toronto distrib KinoSmith. All of the major Canuck distribs took a pass on the project.

The filmmakers have taken a guerrilla approach to the marketing -- Chang has crisscrossed the country appearing at as many screenings as possible to field questions from audiences, and the film has benefited from strong critical support.

But "Yangtze" didn't have even a trailer to support its launch, and little money was spent on prints and advertising. Even producer Mila Aung-Thwin of EyeSteelFilm admits everyone involved has been surprised by the boffo ticket sales. The pic basically found its own audience.

"We tapped into this market that we didn't even know existed," Aung-Thwin says. "It's people who have a desire to travel to China, the same people who want to go on that cruise, and they're middle-aged to retirees. It skewed significantly older and more intelligent."

It also didn't hurt that China has been in the news, with the Olympics and the strife in Tibet. But the bottom line was that auds liked the film -- a rare thing for an English-Canadian release.

The film, which also played at Sundance, continues to have legs, especially outside major cities, and is now set to begin its U.S. run via Zeitgeist Films, starting April 25 in Manhattan. Zeitgeist co-prexy Nancy Gerstman has high hopes for the pic, noting that her company has done well with a couple of previous Canuck docs, "The Corporation" and the China-set "Manufactured Landscapes."

Meanwhile the folks at EyeSteelFilm, who put a lot of their own cash into the film, are just relieved they didn't lose their shirts.

"It was a gamble," Aung-Thwin says. "If we hadn't become one of the most successful English-Canadian films, we would've lost money."