Ghosh's focus on the margins has brought him as much praise as controversy. Born in India and based in New York, he has won France's Prix Medici Estranger, the Pushcart, the Arthur C. Clarke Award for Science Fiction, and Grand Prize at the 2001 Frankfurt eBook Awards for The Glass Palace. But he withdrew the same novel from the Commonwealth Literary Prize in 2001, citing the award's imperial connotations. The book had already sparked furore in India for touching on the members of its military who switched sides to fight for the Japanese in the second world war.

The Hungry Tide raises more questions for Indians. 'Ever since it was released, I've been deluged with mail about it,' he says.

An hour's drive from Calcutta, this shoal of muddy delta islands is where the Ganges, known in Hindu myth as Shiva's heavenly braid, is washed apart into a vast, knotted tangle.

Ghosh, 48, describes it as 'just this huge black hole within the geography of the subcontinent'.

'So little is written about them, so little is known, and yet it's always been one of the great gateways to India. But what's very powerful about the Sundarbans is the way the wildness has always reasserted itself.

'Because it's a wildness that's compounded of many things: the sheer cyclonic brutality of the weather there, the tides which sweep through twice a day, the animals. Everything adds up to a very unusual environmental circumstance. Hundreds of people, for instance, are killed by tigers each year in the Sundarbans, and nobody knows that's actually happening.'

Sundarbans comprise a third of Bengal, yet Bengalis know little about them. Ghosh has been visiting the region since childhood, when his uncle, a headmaster, was a manager of the estate founded on one of its islands by wealthy Scotsman Sir Daniel Hamilton, who tried to establish a utopian society there in 1903.

The Hungry Tide is the story of a young cetologist, Piya Roi, who visits the Sundarbans for her survey of marine mammals. Of Indian parentage, but defiantly American, Piya, meets affluent Delhi-born translator Kanai, who has returned to the islands to visit his aunt, Mashima, for the first time since his uncle, a political radical named Nirmal, died in a bloody stand-off between local government troops and refugees.

Kanai falls for Piya, but she's smitten by Fokir, a fisherman who leads her to the rare Irrawaddy river dolphin, or shushuk. Integral to the inter-generational plot is the 1979 Morichjhapi massacre, in which thousands of impoverished refugees from neighbouring Bangladesh found their way to Morichjhapi, an island set aside for tiger conservation. They were massacred by the leftist Bengal government, which evicted tens of thousands on the pretext of protecting the environment.

'It's a very strange story, because very little is known about it,' Ghosh says. 'It's been completely erased, even in Bengal. Several thousand people died in this event, and it's not spoken of, and so my book has had an enormous impact in Calcutta, and has completely re-opened the story.'

Perhaps the most horrifying aspect of the whole story, Ghosh says, 'is that today the same leftist government is still in place in Bengal - and they've given clearance to a big, rather suspect, company to open up this huge tourism mega-complex right in the middle of the Sundarbans, which will endanger several species and cause irreparable damage to the environment.

'We live at a time when every one of us has to be concerned with our surroundings.'

Ghosh admits that his interest in idealists has coloured much of his work. The key pleasure in writing the novel was spending time with the cetologists who helped inspire a more focused exploration of idealism, 'and the grit that goes into idealism'.

He sought advice from one of the leaders in the field, Professor Helene Marsh, of James Cook University in Queensland, who put him in touch with one of her students, a young New Zealander, Isabel Beasley, a specialist in Irrawaddy dolphins.

Beasley invited him to her base in Cambodia. 'It really gave me a new respect. So many young environmentalists give so much of themselves and really pass completely unrecognised by the world at large. That's something that's very moving to me.'

The Hungry Tide deals with the struggle between tradition and modernity. The words of the German poet Rainer Maria Rilke, who played an influential role in Bengali poetry, resonate throughout the novel.

'Rilke really made me think about what's precious about the world and what you have to do to celebrate it,' he says. 'That's what I think we've forgotten, and that's why so many people have begun to think in such extreme ways.

'More than any people anywhere in the world, the people of the Sundarbans have a right to despair, because of their incredible poverty and deprivation. Yet these are not the people who are becoming suicide bombers. One of the things that was so deeply moving to me, is their intense love of what's around them.

'That's what makes me want to write fiction. Fiction is always, irretrievably, about character. It's about people.'