Australia: We came in search of paradise...

...and left it just as we found it. Tom Adair takes the new eco-tour of Brisbane's Stadbroke Island

The Landcruiser bumped to a halt and we – all six of us on the new Kingfisher "City to Straddie" one-day eco tour – gazed back through a gap in the trees. Two hours ago, we had been sitting in the maw of traffic in downtown Brisbane.

Now, here we were off the Queensland coast – another world.

Brisbane sizzled in the distance, a high-rise shimmer. The day before, while I'd browsed in the tourist information shop in Brisbane's main retail drag, one of the assistants, seeing me pause at a rack of North Stradbroke Island brochures, had said emphatically "paradise island" – a phrase so twee that I inwardly groaned.

But here, with the waft of eucalyptus scenting the breeze, the distant murmur of the ocean, and a single dazzling puff of candy-floss cloud in a sky of blue, I was persuaded to concur that this, "the second largest sand-island in the world", is one of Australia's most precious places.

David Threlander, our guide, rolled down his window and grasped a branch. "You can make beer from this," he said, like a man who'd sampled the result. He stroked the bark of a "scribbly gum". "Look at the squiggles, the work of a worm, and, over there – Banksia. Four Septembers ago the fires came, cracking the seed pods. Fire is what the Banksia needs to propagate."

There was propagation everywhere, in profusion, stretching all the way to Brown Lake, a five-minute drive. At its widest point, North Stradbroke island is barely seven miles across (it's almost 22 miles long). Nothing is much more than a hop from wherever you are.

We stared at Brown Lake, flat-calm and warm when you waded in. It was stained by the tea trees that curved around its gently shallow rim. The sepia-tinted water was great for the skin, according to David.

We had been promised a day of nature-spotting, but no one had mentioned cane toads. "Look at this," said Joel, wading from the water, cupping his hands. "There's dozens more." The toad was thumbnail-sized, still evolving. "Chuck it away,' said David, explaining that "canes, fully grown, are a regular menace." He described them, eating stick insects "like chewing a chocolate bar" – which we pondered over damper cake and coffee.

The drive to Main Beach took us close to Mount Hargrave (barely a 700ft blip) and to the wide blue yonder of sky and sea. Scoured by breezes and planed by the tides, the broad golden swathe of pure sand abutting the gleam of unbroken ocean, was perfectly empty, or so it seemed.

There, parked in glorious isolation, we flung the doors wide and dashed for the waves to cavort like exhilarated school kids. I scanned the horizon for humpbacked whales. "They mostly come between June and November," David said, as if reading my mind.

"A couple of years ago I watched them from here, just 100 metres off shore. One even calved here." He dug up a cockle, absent-mindedly, with his toes. When he lifted it up, it opened its shell and spat at him. "That's what they do," he laughed. "Self-protection." We watched it burrow beneath the sand to disappear with a soundless suck. The scene was pristine, almost abstract: a band of sky, beneath which the dunes and beach and ocean were broken only by a scattering of oyster-catchers and gulls, and the sea's soft tinnitus as our soundtrack.

Barely five miles, and half an hour later, at Point Lookout, life by comparison seemed hectic. A backpackers' hostel and trickle of B&Bs were served by a café or two, a takeaway, and a grocery store tucked under the shade of the headland. Near the toilets, the path was occupied by a dozing blue-tongued lizards, 10 inches long, each keep one scummy, vaguely hung over eye on you.

Ahead lay the Gorge Trail and Frenchman's Bay – "the most photographed beach in Oz," according to David. Beyond us, a sloping flank of solid rock formed a perilous grandstand on which to perch, and from which to "ooh" and "aah" at manta rays and dolphins, and at the specks of baby green turtles riding the wave-surge into the narrow tapering entrance.

We drove due west to Flinders Beach to enjoy a lunch of salad and steak, (David barbecued; we swam). There, in the trees behind the dunes, I watched a goanna, two feet long, creep up through the branches of a tea-gum, flicking its tongue. The accruing impression of Stradbroke Island as a latter-day eco-Eden was undeniable.

To keep it that way requires a tricky balance between the growing trends of tourism and nature conservation. David told us that fewer than 3 per cent of Brisbane's population had ever been here. The other 97 per cent, as we witnessed later, were missing the sight of koalas earthbound, trundling in search of more luscious bowers of eucalyptus, and the scene, just outside Dunwich, the island's town, of flying foxes draped like duffel bags in the trees.

Even the return ferry journey to Cleveland provided appearances by a bull shark, and the day, as we closed in on Brisbane, veered towards afternoon tea at Indigiscapes, Australia's first environmental centre for indigenous plants. There they walk you through the gardens to the background sounds of a lorikeet and water birds, and serve scones with lemon-myrtle butter and bush-tucker jams.

By 5pm David had dropped me outside my hotel, where I'd been picked up just 10 hours before. "Door to door delivery," he grinned. "The tour that delivers." You couldn't argue.

Compact Facts

How to get there

Tom Adair travelled to Brisbane with Qantas Airways (qantas.com), which offers return fares from £1,095. He stayed at the Sofitel Hotel (00 61 7 3835 3535; sofitelbrisbane.com.au), which has superior double rooms from £208 per night. Straddie Kingfisher Tours (00 61 7 3409 9502; straddiekingfishertours.com.au) offers the "City to Straddie" 4x4 Eco Tour for £117 per adult, £83 per child.

Further Information

Tourism Australia (australia.com).