One's long and the other's short, but both are spectacular.
On Tasmania's Franklin River, there's a meditative rhythm to paddling a raft. We've been here for nearly a week, drifting through the heart of the Tasmanian Wilderness World Heritage Area. A lyrebird has just serenaded us from a beach, and only a couple of nights ago I woke on the riverbank surrounded by a galaxy of glow-worms.
Rapids churn and then flatten as mountains stand tall around us, equalled only in scale by the legends that accompany this river. Scene of a famous blockade in the early 1980s that helped swing a federal election, the Franklin was also once named by a leading US adventure magazine as the greatest rafting river on the planet.
Cross the country and you discover that the Franklin isn't Australia's only great white-water challenge. In north Queensland, fed by the nation's most voluminous rains, the Tully River was also once named one of the world's 10 best rafting rivers by the International Rafting Federation.
Together these two torrential waterways form the long and short of Australian rafting - the Franklin, a committing river journey across more than a week of wonderment; the Tully, a fast and furious blast of a few hours through a succession of rapids. Neither river is a place for the inexperienced, but guided rafting trips bring them into the reach of most.
Each guide brings their own personality and tricks to the river.
A rafting trip on the Franklin River has a matchless sense of isolation. From the moment you launch on the Collingwood River, a few kilometres upstream from its junction with the Franklin, you're entering a catchment without any cultivated land and not a single house or building. It feels puzzling that Hobart could be little more than 100 kilometres away.
There are four major gorges along the Franklin - Descension Gorge, Irenabyss, the Great Ravine and Propsting - with wildly contrasting characters. The world seems to stop inside the deep and calm Irenabyss, where even the river seems motionless as it flows between high cliffs.
The Great Ravine, on the other hand, is a place of might and muscle. Powerful rapids with ominous names such as Churn, Corkscrew and Thunderush fight their way through the river's great pinch point, forcing rafting parties to portage much of the ravine, scrambling along the riverbank or cliff ledges as guides toss, push and pull rafts through the turmoil. It can typically take a full day to navigate this single seven-kilometre-long gorge.
Between rapids, the water and heart rates settle and the river's immense beauty comes to the fore. As you tumble out of the final rapid in Propsting Gorge, you find yourself at Rock Island Bend, scene of the emblematic Peter Dombrovskis photo - perhaps the most recognisable nature image ever taken in Australia - used to help save the Franklin from dams in 1983. Elsewhere, you can step into the moss-coated Lost World slot canyon and float past Kutikina Cave, where hundreds of thousands of Aboriginal artefacts were found in the late 1970s. It was one of the richest archaeological sites ever discovered in Australia and helped secure World Heritage status for the area.
By its nature, a Franklin River journey is committing, with everything you need for the eight to 11 days packed into your raft, which, depending on water levels, you might at times be dragging over rocks and logs by hand.
Nights are spent in the open air, beneath a ceiling of stars (or a tarpaulin if rain looks possible) or, on one memorable evening, in cliffside caves and rock platforms at Newland Cascades, beside the river's longest rapid. This camp also heralds the moment that the river flattens and widens, and the journey relaxes into a peaceful float through one of Australia's greatest wildernesses.
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In contrast, things rarely settle on the Tully River as it squeezes through Tully Gorge. This wild ride through Jirrbal and Gulngay country, along the edge of the Wet Tropics World Heritage Area, sets out from just below the Kareeya Hydro Power Station, with the river's flows dictated by its water releases. In little more than three hours, rafts plunge through more than 45 rapids, from the rude awakening of Alarm Clock, a grade IV rapid immediately below the put-in site, to a weir that has only one safe, narrow line for rafts.
As on the Franklin River, a guide sits at the rear of the raft, steering the boat and calling the shots. Each rafter wields a paddle, employing it in response to calls from the guide - "forward paddle", "back paddle" and, in those moments of need and excitement, "get down". Instructions are delivered as calmly as the flat stretches of water between rapids, and each guide brings their own personality and tricks to the river - at one point, our guide steps unseen from the raft onto a boulder in the middle of the river, waving from the rock as the raft spins past with the current, before leaping back in and resuming control.
Staying dry is not an option, with water pouring over the sides of the raft and even from above as you exit one rapid and plough straight into the base of a waterfall, which pelts helmets, shoulders and the raft with bullets of water.
It's Australia's wildest water ride, but there are quiet moments between the lurches, times to sit back and soak in the beauty of the teeming rainforest - a world of kauri pines and strangler figs - that smothers the riverbanks and cliffs.
And then it's game on again - paddles to hand, a call of "hold on", the river returning to rapids. It's about to get wild once more.
Franklin River rafting trips depart from either Hobart or Launceston and local operators include Tasmanian Expeditions (tasmanianexpeditions.com.au), which has trips starting from $4195.
Rafting trips on the Tully River, departing from Cairns, Mission Beach or Tully, are run by Raging Thunder (ragingthunder.com.au) and cost from $225.
The writer rafted courtesy of Tasmanian Expeditions and Raging Thunder.