Available on DVD: “Last Call at the Oasis”

Jay Famiglietti, one of a handful of expert witnesses in Jessica Yu’s Last Call at the Oasis, is a thoughtful scientist with an engaging manner who specializes in water. In particular, he studies — and tries to raise public awareness about — the rapid depletion of water supplies caused by agricultural overuse, rampant development and global climate change. His analyses are thorough and clear, and he presents them, at public meetings and straight to Yu’s camera, with good-natured patience. For the most part, that is. At one point, contemplating a future of unchecked consumption and political paralysis, he sums it all up in blunt layman’s terms: "We’re screwed."

That might serve as an alternative name for Yu’s film, or even for the genre to which it belongs. The global-catastrophe documentary is a thriving form these days, as the apparent unsustainability of human life has emerged as fertile ground for cinematic journalism. Last Call at the Oasis follows Payback, Surviving Progress and The Island President — to name only some of the most recent releases — in a drumbeat of elemental doom. The food we eat, the stuff we buy, the air we breathe, the fuel we burn, the water we drink: it’s all killing us!

Yu, who has directed scripted television episodes as well as documentaries, wraps a lot of bad news into a slick, informative, fast-moving package. Dwelling mostly on the United States, with forays to Australia and Israel and brief glances at Asia, Africa and South America, she weaves local stories of drought and pollution together with larger-scale explanations of the worldwide water crisis.

Dr. Famiglietti and others (notably Peter Gleick of the Pacific Institute) take us to the drying-out regions of the West, where competition for water has a long history (as fans of Chinatown may recall). Fast-growing Las Vegas, as it drains nearby Lake Mead, contemplates a pipeline to pull water from ranch land in northern Nevada. Conservationists in the San Francisco Bay Area who want to restore rivers and protect fish incur the wrath of farmers in the Central Valley of California, and the specter of less snow in the mountains haunts everyone.

In addition to scarcity, there is contamination. Tyrone Hayes, a biologist, shows us mutant frogs, their endocrine systems scrambled by pesticide-borne chemicals. Erin Brockovich visits towns with terrifying rates of cancer, continuing the work that inspired the Oscar-winning film starring Julia Roberts (a few clips of which are shown). Lynn Henning, a Michigan farmer, monitors the toxic runoff from lagoons full of cow manure from huge industrial feedlots.

Meanwhile, we clog the waste stream with empty plastic water bottles and persist in believing that there is a never-ending supply of this essential substance. The calm, knowledgeable voices of the experts — also including the journalist Alex Prud’homme, whose book The Ripple Effect is cited as an inspiration in the opening credits — make Last Call at the Oasis especially scary. Nothing is more unnerving than predictions of an apocalypse delivered by a reasonable person in friendly, conversational tones.

The question is whether anyone is listening, and it is a question that always nips at the heels of documentaries like this one. One way the question is answered — or perhaps finessed — is by the optimistic, encouraging tone that tends to sneak in at the end. Most examples of the "We’re screwed" documentary, in other words (at least in the American version of the genre), end on a note of "Yes, we can."

Some of the optimism in Last Call at the Oasis comes from a gratifyingly unlikely place — the Middle East, where shared water problems have led to cooperation amid otherwise intractable political conflict. There is also a measure of hope to be gleaned from Yu’s interview subjects, though less from what they have to say — which is pretty grim — than from their seriousness and dedication.

However frustrated they may be by political paralysis, corporate trickery or plain human stupidity, none of them seem inclined to give up. When they do, we really will be screwed, and we won’t have or need movies like this to tell us so.