In the 20 years since I first published my memoir Land’s Edge, I’ve stayed close to the water, living and working where desert meets sea in my native Western Australia. The littoral, that peculiar zone of overlap and influx, sustains my spirit and fuels my work. I’m still pulled between the sensual assault of the outdoors and the sedentary life of reflection. To go a day or two without seeing, feeling and smelling the ocean wouldbe as disorientating as being without a book or an hour’s privacy.

When I wrote that modest coastal memoir, I was the father of young children, eager to introduce them to the freedom and the privilege of a life at the water’s edge at the bottom of the world. It was what I knew and took for granted as a boy. Like me, my kids inherited a clean, living ocean. They enjoyed a simple, small-town existence on a wild coastline and I tried to make plain to them what a privilege that was, because it is a luxury to be able to wander free and barefoot on an empty beach, to swim with a sea lion, snorkel in a coral lagoon and catch dinner at the end of an ordinary school day. Those children are adults now. One is a parent.

This summer, I took my granddaughter into the sea for the first time. Her whole body shuddered with the strangeness of it, the surge and light and noise, the spill across her delicate skin. What a thrill it is for a sun-damaged old beachcomber to pass on such a life as a birthright. Yet only a fool could suggest that this little girl’s coastal inheritance is secure.

Sadly the world’s oceans are in peril. Ninety per cent of pelagic fishes and sharks are gone. Human beings are eating themselves out of house and home, consuming as if there was no tomorrow and not even our remote stretch of coast is immune.

Hunting and gathering are in my blood but I’ve lived to witness a diminution in the seas around me; I’ve had to boat and swim further and longer to find fish. In the 1990s, I swam across local reefs without abalone, visited submarine pinnacles without snapper, walked beaches festooned with plastic.

Australian waters had begun to feel the effects of shark-finning, drift nets, oil spills and the voracious incursions of the oil and gas industries. The emerging scientific consensus was that, globally, too many species of fish were either fully exploited or being catastrophically overexploited. You didn’t need to be any sort of boffin to know that something was wrong in our seas; every time you wore a mask and fins, the evidence was there in front of your face – more and more of less and less. It was futile blaming faceless strangers. We were all taking too much. It was time for me to act as if there was a tomorrow, as if my actions bore consequences, so I changed my ways, looking more and taking less.

Yet the fragile coast was in more trouble than the restraint of a single middle-aged man could remedy. The oceanic dead zones of Europe and Asia, the plastic gyres of the Pacific, began to haunt me. Unless whole cultures changed, these horrors would be universal; this would be our legacy. This is how I became an activist. To the battle-scarred Birkenstockers of the environmentalist movement, I was a redneck. After all, everything I knew about the sea I had learned with a spear in my hand. The actual rednecks who were my neighbours thought I’d lost my mind. If to change your mind is to lose it, perhaps they were right.

A decade after I first swam with whale sharks at Ningaloo, developers were lobbying to build a marina resort there. Australia’s longest fringing coral reef, it hugs the shore along the red desert for 200 miles. You can swim with a manta ray as a kangaroo cools its heels at the water’s edge a few yards away. There is no place in the world quite like it. Sustainable ecotourism was just finding its feet in the region, thanks to the regular presence of the enormous, gentle whale sharks. From the world over, visitors were coming to Ningaloo, not to take but to look. Dredging and blasting this habitat would have been a disaster but the resort’s backers saw golf courses in the desert, speedboats, cocktails by the pool, a sort of Costa del Sol where whale sharks were an optional extra.

As hard as it is to believe now, their plan had great support in parliament and many boosters in the media. Western Australia is a frontier state, riding boom after boom. Development is regarded as virtuous, almost messianic. To express any reservation about unfettered “pro - gress” is to declare oneself a heathen, a citizen of insufficient revolutionary zeal. With the government and media in thrall to big business, the odds of halting or even modifying a proposal such as the one at Ningaloo were remote.

Those of us who fought the defining struggle to save Ningaloo Reef didn’t expect to win but those ranges and corals were too precious to surrender without a struggle. Naively, I assumed my role would be discreet – as a supporter behind the scenes – but I was wrong.

In middle age, a privacy freak with no experience of either advocacy or politics, I was compelled to acquire a thick skin and a fresh suite of skills. I write novels for a living. In all my working life, I hadn’t collaborated with a soul; I’d never been part of a team or shared an office. I’d never submitted to any sort of discipline but my own, yet here I was, all of a sudden, pressed into service as the most visible member of a motley team made up of citizens of every age and class and political view. With little more than raw passion and a fax machine, we were trying to stop a juggernaut. Every week, there were more of us. We told our story the best we could and in time the campaign gained momentum. Once the reef caught people’s imagination, the tide turned.

For two years, I more or less gave up being a writer. I wrote only press releases, begging letters, strategic notes. I helped plan actions and stunts, met politicians and scientists, made speeches at town halls and too often found myself in front of TV cameras. I took film stars swimming with manta rays, tried to introduce the local rich to the novelty of philanthropy and posed like a prat for hundreds of photos. I made many friends and a few significant enemies.

I resented the lost time, the lazy journalists, the somnolent MPs, the silly theatre of it all, but I think of that period as a late-life education in civics. What it taught me was not always uplifting. To gain any sort of media attention, a social or environmental issue requires a circus, a celebrity or an act of violence.

We tried only the first two. And, yes, money does talk. However, once you get direct access to ordinary citizens, you discover that the victory of selfish consumerism is not yet complete. Despite the numbness and nihilism in our culture, there is still an instinct for justice and proportion, self-restraint and an abiding sense of the common good. I’m no utopian but I found that, deep down, human beings love the world that sustains them. Given honest information and a bit of respect, they will act to defend it, even for the sake of unborn strangers.

Somehow, we prevailed. In saving the reef, we rewrote the laws for coastal development. In 2011, Ningaloo was added to the World Heritage register.

Since the campaign, I have tried to return to the reclusive life I enjoyed before, but one contest seems to lead to another and I find myself enmeshed as a reluctant advocate for the marine environment. It’s a grind at times but it’s heartening to be part of a genuine sea change. This year, Australia is poised to declare a chain of marine sanctuaries from the Southern Ocean to the Coral Sea. The initiative has its detractors and scaremongers in parliament and the press but the idea has broad public support. The mood has shifted; folks have moved on.

Now and then, it’s worth being reminded of just how far a culture can shift within a generation. I think of a hole I once swam in near the Montebello Islands, to the north of Ningaloo. It’s a crater, about 1,000 feet across, left by a British atomic bomb in 1952. A strange place for a snorkel, I admit it. Not much to see down there but glassy sand and weird, white worms. Only a few years before I was born, it seemed necessary to blow islands from the sea and irradiate entire ecosystems. Apparently, the future depended on it. Today, those islands are registered sanctuaries for dugongs, whales and rare marsupials; its birds and corals are protected by law.

The shift of mindset required to achieve this was immense and sobering. It seems odd to say that a swim in a once-radioactive hole can be restorative, but when change feels too slow and the losses mount up week by week, I recall that eerie hole and how far we’ve come since it was gouged into the sea.

Tim Winton’s most recent work is the play “Signs of Life” which premiered in 2012