Fiordland Fast Facts
421 metres at its deepest. 40 kilometres long. Three arms, one cove, and no road in. The numbers and the stories behind New Zealand's deepest fiord, from the people who work on it.
By the Numbers
Doubtful Sound is 421 metres deep at its deepest point, which makes it New Zealand's deepest fiord. That is deeper than the Eiffel Tower is tall, and it is why the water beside the boat looks black rather than blue.
The depth is only half the story. Rain draining off the rainforest, and the outflow from the Manapouri power station at Deep Cove, lay a layer of tannin-stained fresh water a few metres thick on top of the seawater. It dims the light below, so species that normally live far deeper, including black coral, grow within reach of divers. The fiord is famous among marine biologists for exactly this.
From the deck you will not see any of that. What you will see is a fiord where the sounder reads hundreds of metres a stone's throw from the shore.
About 40 kilometres from Deep Cove at its head to the Tasman Sea, roughly three times the length of Milford Sound and more than ten times its area. Three side arms branch off the main fiord: Hall Arm, Crooked Arm and First Arm, each a fiord in its own right that a day cruise rarely has time to enter.
That scale is the practical reason we run an overnight cruise rather than a day trip. With a night at anchor there is time to get into the arms, out to the seaward end where the fur seals haul out, and back, without watching the clock. It is also why you can spend two days here and see almost no other vessel.
Captain James Cook sailed past the entrance in 1770 and named it Doubtful Harbour. He was doubtful that, once inside, he could sail back out against the prevailing westerly winds, so he did not go in. Later charts changed Harbour to Sound, and the name stuck.
Strictly, Cook's successors got it wrong. A sound is a river valley drowned by the sea; a fiord is a valley gouged out by a glacier, which is what gives Doubtful its sheer walls and its depth. Every "sound" in Fiordland is really a fiord, and the region's name quietly admits it.
Its Māori name is Patea, and the official name today is Doubtful Sound / Patea. On the water, the crew tend to just call it Doubtful.
There is no public road, which is the single biggest reason the fiord is so quiet. From Pearl Harbour at Manapouri, about twenty minutes south of Te Anau, you cross Lake Manapouri by boat to West Arm. A coach then climbs over the Wilmot Pass and drops down through rainforest to Deep Cove, where MV Tutoko II boards.
The Wilmot Pass road exists only because of the Manapouri hydro-electric scheme. It was built in the 1960s to haul machinery between Deep Cove, where it arrived by sea, and the power station under construction at West Arm. It connects to no other road in New Zealand, and the power station's tailrace still discharges into Deep Cove today.
Milford Sound, by comparison, is reached by a sealed highway from Te Anau. The two fiords are roughly two and a half hours apart by road, and many of our guests do both; the Milford vs Doubtful comparison covers how.
A resident pod of bottlenose dolphins, one of the southernmost resident populations in the world, lives in the fiord year-round. New Zealand fur seals haul out on the rocks towards the seaward end. Tawaki, the Fiordland crested penguin and one of the rarest penguins anywhere, come ashore to breed in the rainforest from July to November.
None of them keep a timetable. What the overnight format gives you is two days and a night in their territory instead of a few hours, and a crew who have been reading this water since 1998. When the dolphins do come to the bow, twelve people see it from the rail together.
In the south-west corner of New Zealand's South Island, inside Fiordland National Park, the country's largest national park and part of the Te Wāhipounamu South West New Zealand World Heritage Area. Departures leave from Manapouri, about twenty minutes from Te Anau and around two and a half hours' drive from Queenstown.
The best time to visit depends on what you want to see, and the packing list is short. Both are worth five minutes before you book.
See It for Yourself
Forty kilometres of fiord and three side arms do not fit into an afternoon. The Doubtful Sound overnight cruise aboard MV Tutoko II takes a maximum of twelve guests, with kayaks, fishing, a freshly caught dinner and a night at anchor where the day boats never go.
From $935 per person · Max 12 guests · Departs Manapouri year-round
Good to Know
How the two fiords compare, and how to fit both into one Fiordland itinerary.
Read the comparison
Summer light, winter snow, spring waterfalls and tawaki season, month by month.
Pick your season
Layers, footwear, rain gear and what we already have on board. The practical packing list.
See the packing list