Anyone who travels to an underdeveloped country has to confront the conflict between the desire for an “authentic” view of the countrypreferably with Arcadian vistas and unadulterated cultural traditionsand the reality that many of the locals exist in miserable living conditions.

A similar contrast is at work in Up the Yangtze, the Chinese-Canadian filmmaker Yung Chang’s fine, slow-burning documentary, in which we see the evolving landscape of the Yangtze River through the eyes of tourists looking for the bygone China of yore and of impoverished strivers trying to survive in the cutthroat capitalism of today’s reality.

With a level gaze and an utter lack of sentimentality, Up the Yangtze documents the upheaval wrought by the engineering project known as the Three Gorges Dam. The project, begun in 1994 and slated for completion in 2011, was a long-cherished dream of Mao Zedong, the film notes. And it is massive: It will be the largest hydroelectric facility in the world, will generate 22,500 megawatts of power and, most crucially to this film, involves displacing more than two million peoplemostly poorwho scratch out a living along the river.

To tell the story of the most ambitious change to the landscape since the Great Wall, Chang trains his lens on a luxury cruise ship that takes Western tourists up the flooding river to see the last of the rural culture that is being eradicated, one rising meter of water at a time. We meet two entry-level cruise ship employees, Chen Bo Yu and Yu Shui. Both are teenagers who hail from families that are feeling the effects of displacement. But beyond that, they’re completely different: Chen Bo Yu is a good-looking but vain 19-year-old pampered by his grandparents, while the shy Yu Shui is a mere 16, the eldest child of illiterate farmers who subsist on the river. She wants to continue her education, but her desperate (and apologetic) parents insist that she go to work on the boats.

Fortunately, this documentarywhich took two honorable mentions at this year’s Full Frame Documentary Film Festivalis not the sort of film that operates by pitting its characters against each other. Although our greater sympathies are with the girl, both teenagers suffer the indignity of being renamed immediately upon arrival at their jobs: Yu Shui becomes “Cindy” and Chen Bo Yu becomes “Jerry.” (This practice is common at Indian call centers, too; perhaps America’s number will be up when the Indians and Chinese no longer think it’s necessary to do this.)

China has something of a tradition of sacrificing many for what is purportedly the greater common good, but it can be all too easy to make generalizations about a populace’s willingness to endure great suffering just because the emperor or the Party says so: Chung gives us a remarkable scene of a weeping river refugee who says between convulsive sobs, “It’s hard to be a human, but being a common person in China is even harder.” This sequence also shows Chinese authorities removing angry senior citizens by force.

We’re going to see a lot of China next month when the Olympics get under way. In anticipation of its global coming-out party, Chinese authorities have spent years scrubbing away at Beijing and its surroundings, from making pollution and poor people disappear to banning dog meat from the city’s restaurants. Up the Yangtze evinces little nostalgia for the China of yore (the thoroughly Westernized Chang has only heard about the old country from his grandfather). Instead, the film looks at the reality: China is a modern industrial powerhouse, and it is here to stay. One of the film’s most lingering images is one Chang says he captured on his video-phone, that of a small girl dancing at a New Year’s celebration, wearing sunglasses at night like the hedonistic rave chick of tomorrow.

Up the Yangtze opens Friday at the Chelsea.