The river, Guinness-black, seems utterly still, its surface polished obsidian, reflecting every detail of the early morning scene. A dense fringe of tea trees, celery-top pines and tall blackwoods contemplates a mirror image whose clarity will be broken only briefly by the dip of our paddles. The fortunate souls in the other kayak inform us over breakfast that they have been paddling with platypuses; well, with a V-shaped ripple, anyway.
Across the sunlit water, Discovery, the 32m-catamaran that has brought me and my husband down the 60km expanse of Tasmania's Macquarie Harbour and into the Gordon River, dwindles from grand and looming to tiny and insignificant. Once aboard, we'll readjust the focus, watching the landscape gliding past, gift-wrapped: a backdrop for champagne and turned-down beds, for Mozart murmuring over the public-address system, and a top chef in the galley. There's even a captive, on-board naturalist to set right those of us who can't tell our currawongs from our quolls. But for now, it's easy to sustain the illusion that we are alone in what the brochure describes as one of the world's last pristine, temperate wildernesses.
Tasmania intends to keep it that way. The coming season sees Discovery licensed for the first time since she was launched in December 2004 to take passengers 20km up the Gordon River from Macquarie Harbour in the island's south-west to the Franklin River mouth. This February voyage of ours is something of a reconnaissance. Further upriver, the banks close in, wisps of cloud scarfing some of the oldest trees on earth.
We disembark at Heritage Landing to admire a copse of Huon pines; some of these monsters have taken 2,000 years to mature. With relatives flourishing in Chile, the southern beeches stand here as proof of Gondwanaland, says our naturalist: relics of that unimaginably distant time before the continents drifted apart.
Matters have not always rested quite as undisturbed. Convicts chipped away at these trees and limestone cliffs; from the 1820s, an army of loggers ventured ever further into the wilderness to supply a Huon pine industry that lasted 150 years. Asked about trucks sporting the legend: "'Doze in a Greenie; Help Fertilize the South-West", Captain Troy Grining recalls the biggest and most divisive conservation battle in Australian history. In 1979 Tasmania's Hydro-Electric Commission unveiled plans to build a dam and power station which would have flooded 37km of the Gordon River and 33km of the Franklin. The prospect unleashed four years of furious exchanges and public demonstrations, pitted Tasmania against the Australian Government and bitterly divided the tranquil community of Strahan.
Troy points out a couple of rotting piles, half hidden in the river bank, relics of the proposed dam and witnesses to an epic "Greenie" victory. When the federal government declared a great swathe of the area to be a national park and nominated it for Unesco World Heritage listing, Tasmania's premier reacted swiftly by sending in the bulldozers. The subsequent blockade, mounted at the end of 1982, lasted three months. It resulted in pitched battles, countless injuries and 1,300 arrests of protesters, including the carefully orchestrated "nicking" of the British naturalist David Bellamy. Today the Tasmanian Wilderness World Heritage Area covers almost 20 per cent of the state, making this a place of extraordinarily rich opportunities for walkers, as we are later to discover in the gorgeous Cradle Mountain region. Perhaps the conservationists' greatest achievement is the fact that more than 140,000 people a year come to visit the wilderness.
Without tourism, stripped of its former industries, Strahan would wither. We earlier disembarked at the wonky jetty which served East Pilling, a ghost settlement where the North Mt Lyell Copper Company once employed 600 people. All that remains is a brick kiln, a couple of old boilers and the carcass of a Pullman carriage, the forest thrusting green fingers through its timbers. The Grinings, a fifth generation family of Strahan millers, miners and log men, had already taken the eco-route; from their boatyard, they established the first pleasure cruises here in 1896. Discovery, their latest venture, is a dream: her 12 cabins well-appointed - our queen-sized bunk was occupied a year earlier by Crown Prince Frederik of Denmark and his Australian princess, Mary. The service is outstandingly friendly and informal and the food sensational. Looking back on days which start with crayfish omelette, and which end with lobster broth, fragrant with saffron and cognac, makes me want to put my head on the kitchen table and cry.
Something about being moored off Sarah Island - from 1822 to 1833 one of Australia's most notorious penal settlements - gives a slightly queasy edge to quaffing champagne and lobster bisque. "It was a graveyard; you were buried alive," says local thespian Richard Davey, an expert on the history of the six-hectare island; he fills us in on bloodcurdling tales of floggings, murder and cannibalism, of imprisonment for crimes as heinous as stealing a bunch of parsley. It's a day of peerless weather; the sunshine, the wild flowers, the wallaby hopping about in the undergrowth all conspire to rob the imagination of such scenes. Near the ruins I pick up a brick and wonder whose thumb made the print just discernable in its surface.
An alternative view, fashionable among contemporary historians, maintains that though the beginning of Sarah Island's story is shot through with brutality, the widely held picture of unremitting depravity and woe is misleading, largely the result of well-meaning propaganda. By 1828 the settlement operated the most productive shipyard in Australia. Their industrial skills enabled the convicts to negotiate and even to establish pockets of control. By the end, says our storyteller, its occupants were describing the penitentiary as a comfy billet. The last ship launched from Sarah Island, the Frederic, was seized by the 10 convicts who had built her and sailed 16,000km to Chile. I find I can face the evening's truffled quail pie with equanimity.
Our last morning sees Discovery skimming confidently over the current which rips through Hell's Gates, the fangs of rock which guard the 75m-wide entrance to Macquarie Harbour. Beyond the breakwater the Indian Ocean pounds Tasmania with huge waves, driven halfway round the globe by the Roaring Forties. But most of our two-night voyage round the harbour and upriver has been a lot calmer. In Birch's Inlet, the fragility of the wilderness comes home in the shape of a little, flying jewel of a bird, scarcely bigger than a budgie. Fewer than 200 orange-bellied parrots are thought to survive, which makes them much rarer than giant pandas or Siberian tigers. Their problems lie in wait at the other end of their migratory path, in Victoria and South Australia where rival feeders, indifferent politicians, foxes and feral cats abound. Here, isolated in a breeding sanctuary among the button-grass plains, they are safe.
I watch a young bird being ringed and set free to take its chance in a hostile world, one small reason why the World Heritage Committee describes the Tasmanian wilderness as "one of the most precious places on earth".
The writer travelled with Audley Travel (01869 276 345; www.audleytravel.com) with assistance from Tourism Tasmania (00 61 3 62 308 235; www.discovertasmania.com.au). Audley offers a similar two-week tailor-made trip to Australia, including Tasmania from £2,535. Tasmania is accessible via Melbourne or (more distant) Sydney, both served byQantas (0845 774 7767; www.qantas.com.au). A wide range of other airlines serve one or both cities via the Middle East, Asia or America. From Melbourne and Sydney, Qantas, Jetstar (00 61 3 8341 4901; www.jetstar.com) and Virgin Blue (00 61 73 295 22 96; www.virginblue.com.au) fly to Hobart and Launceston.
To reduce the environmental impact, you can buy an "offset" from Climate Care (01865 207 000; www.climatecare.org). The environmental cost of a return flight from London to Hobart, in economy class, is £43.50. The money is used to fund sustainable energy and reforestation projects.
A ferry (00 61 1800 634 906; www.spiritoftasmania.com.au) serves Devonport from Melbourne with departures each evening in both directions, and some daylight sailings at peak times.
World Heritage Cruises (00 61 3 6471 7940; www.worldheritagecruises.com.au) offers two-night Tasmanian Wilderness Escape cruises from A$1,995 (£800) per person, full board, including excursions and activities.
In Tasmania by Nicholas Shakespeare (Vintage, £8.99).