Minamata is not a masterpiece and there are one or two cliches here about western saviours and boozy, difficult, passionate journalists who occupy the perennial Venn diagram overlap between integrity and alcoholism. This movie’s producer-star Johnny Depp has form on this score, with his starstruck impersonation of Hunter Thompson. And once again, he has chosen a role in which he wears a hat indoors. But Minamata is a forthright, heartfelt movie, an old-fashioned “issue picture” with a worthwhile story to tell about how communities can stand up to overweening corporations and how journalists dedicated to truthful news can help them.

Depp plays real-life US photojournalist W Eugene Smith whose glory days were in the second world war and the decades following, working for Life magazine in that now-forgotten era when analogue cameras were incapable of lying and magazines with compelling photos could command newsstand sales.

The drama finds him in his declining years, drunk, depressed, impossible to work with – and of course ripe for Hollywood-style redemption. Apparently by chance, he finds himself befriended by Japanese-American Aileen (Minami Hinase) who alerts him to an environmental atrocity in Japan that he could do something about, if he chose to rouse himself from his grumpy self-indulgent ennui. In the coastal town of Minamata on Japan’s south-western coast, the Chisso corporation has been dumping mercury waste into the water, which is poisoning the fish and then the humans who eat them – causing horrendous disfigurements in men, women and children.

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Truculent, impulsive Smith barges into the office of his editor (a straightforward, American-accented role for Bill Nighy) demanding to be sent to cover the story and his exasperated boss agrees. From there, Smith finds a community who treat him with respect and politeness, though some are suspicious of a brash foreigner who may simply make things worse and alienate a powerful employer that could turn against making any settlement.

Of course, the hard-nosed professional in Smith knows that pictures of sick children, carefully and tactfully managed, are going to deliver the biggest punch and he became famous for a picture that heartbroken and intensely private parents were at first reluctant to give him: Tomoko Uemura in Her Bath, the Pietà-esque black and white photograph of a mother cradling her sick daughter in a traditional Japanese tub. Director Andrew Levitas gives us a context-free glimpse of this challenging image at the beginning of the film and builds to its eventful composition as his emotional finale.

Perhaps its use here is a little glib, but the film does at least emphasise a kind of journalism that is at the service of the people that it depicts. And it reminds of a time when the environmental debate was about pollution not climate change – although that issue has not by any stretch gone away. Over its closing credits Minamata concludes with a list of grotesque and often unpunished “spills” including Bhopal, Deepwater Horizon and more. Perhaps these are the microcosmic crimes and our fossil-fuel use is the larger, global issue. At any rate, Minamata is a decent reminder of what is still to be done.