The Darwinian phrase “survival of the fittest” has a twofold meaning in this documentary by Hubert Sauper about the miserable conditions in the Tanzanian communities surrounding Lake Victoria in east Africa. It refers first to the ecological disaster that resulted from the introduction, whether accidentally or intentionally, of the Nile Perch into the lake–a predator that killed off all the native species. But the words also apply to the appetite of westerners for the fish, and the creation of factories near the lake to prepare the catch for transport elsewhere–the exploitation, in other words, of the resources and people of the Third World by the powerful. And that’s but the tip of the iceberg. The transformation of the area has also involved the abandonment of the rice farms in the surrounding region, the concentration of people in the towns, resultant famine, the destructive effects of AIDS, and a local population sunk in poverty, disease, prostitution and drugs. Local authorities and international conferences dither as the community suffers and dies, contributing even further to the chaotic situation by turning a blind eye to the fact that the cargo planes bring in weapons to stoke area conflicts before flying out filled with fish.

“Darwin’s Nightmare” is very loosely structured, covering all the bases in a piecemeal fashion that shuffles the various narrative threads in an apparently arbitrary fashion, without much sense of organization. But the cumulative effect is striking, and the filmmakers’ invitation that viewers effectively put the strands together for themselves is actually rather refreshing in an age when most documentaries pound you over the head with their theses. The film is especially impressive in personalizing the story by getting locals–sullen street kids, desperate fishermen, beaten-down prostitutes, sad victims of HIV infection, an ebullient factory owner, a cautious minister (who admits that despite the AIDS epidemic, he won’t suggest the use of condoms because they encourage sinful conduct), a hopeful kid who’s escaped the street life and now paints scenes of life in the town, a soft-spoken night watchman at a local institute–as well as outsiders (usually jocular but sometimes ruminative Russian pilots who deliver unidentified cargo and fly out with their planes carrying tons of fish) to open up to the camera with remarkable candor. These parts of the film are deeply affecting–so much so that when, toward the close, it’s revealed that one of the subjects you’ve come to know has died, it carries an emotional wallop. And beside them the larger, contextual material is a mite flat.

But one shouldn’t allow the perfect to be the enemy of the good. Sauper’s film, shot on the fly with a minimum of technical tricks and looking every bit like it, has real impact. And though it obviously concentrates very skillfully on a particular time and place, it also points to larger global issues that should make us all stop and think about our social responsibilities.