A harbour on the edge
Te Whanganui / Port Underwood lies at the south-eastern edge of the Marlborough Sounds, its narrow entrance opening just north-west of Cloudy Bay. Facing south, it is sheltered in most conditions, though a strong southerly can sweep straight in and remind visitors of its connection to the open sea.
The harbour stretches 9.3 kilometres from end to end and spans 3.5 kilometres across at its widest. Steep hills, cloaked in forest and pines, rise abruptly from the shoreline, giving the inlet an enclosed, almost secret feel. Channel depths run between 10 and 20 metres, shoaling close to shore. A tongue of land divides the harbour into two legs, with hidden bays tucked along every reach.
It may lack the broad sweep of Queen Charlotte or Pelorus Sounds, but there’s plenty of room to swing at anchor. With dimensions larger than Bon Accord Harbour on Kawau Island — a place where 50 footers manoeuvre without fuss — Port Underwood provides ample space while keeping an air of intimacy. Along the shoreline, quiet beaches invite exploration, many only reachable by tender or shallow-draught boat.
Layers of history
The harbour’s story is etched both ashore and beneath the waves. In the 1820s and 30s, whaling stations sprang up, John Guard establishing one at Kakapo Bay. By 1840, around 150 Europeans were living here — perhaps the largest European settlement in the South Island at the time.
Maritime history also rests on the seabed. Between Oyster Bay and Whangataura Bay lies a wreck site, accessible only by boat. Just south at Blackball Point, the remains of the Blackball still linger in the shallows. Once a coal hulk towed from Wellington in 1923 for river protection at the Wairau, she never cleared the Wairau Bar. Instead, she drifted around Port Underwood on an inadequate anchor before grounding on the point. Kauri planks and iron were salvaged, the hull was eventually burnt, and fragments of her structure remain visible today.
Modern industry has left its mark too. Mussel farms line several bays, exotic forestry dominates the ridges, and the commercial wharf at Hakahaka Bay services aquaculture. Yet outside these pockets of work, the harbour retains a quieter rhythm: baches tucked among bush, campsites near the water, and a coastline that speaks more of retreat than commerce.
Getting there
Port Underwood sits about 29 NM from Waikawa and Picton marinas — a little under five hours’ sail in a yacht cruising at 7 knots, much quicker in a motor launch. Many skippers prefer this sea run over the demanding roads. The harbour is not completely sheltered, but holding is good.
For trailer boats, Oyster Bay is the main access point, with a wharf, ramp, Diesel BSP Fuels, and limited parking. Smaller craft can launch at Tom Canes Bay, near the harbour entrance, where a sheltered beach makes an easy launching spot.
The road journey is beautiful but not easy. From Picton, Port Underwood Road threads through Waikawa, skirts Whatamango Bay, and climbs steeply before dropping into Oyster Bay. From Blenheim, the road rises sharply out of Rarangi, winding past Whites Bay and Robin Hood Bay before looping north. Recently reopened after slips and flood damage, this Blenheim approach had been closed for some time. Further east, Tumbledown Bay Road edges deeper into Port Underwood, though its narrow gravel makes it slow going and unsuited to trailer-boat launching.
Anchorages and weather
Port Underwood is full of anchorages, from quiet corners to broad open bays. Ocean Bay, with its mud bottom, is renowned for holding. Oyster Bay and neighbouring Hakahaka Bay are well regarded, while Opihi Bay, Ngakuta Bay, Tumbledown Bay, Jerdans Bay, and Pipi Bay also offer secure overnight stops.
Most seabeds are sand or mud, dropping quickly to 10–15 metres. Excessive chain isn’t necessary, but managing scope is essential. Scope is the ratio of the length of anchor rode (line or chain) deployed to the vertical distance from the bow to the seabed. In gusty conditions, a generous scope will help the anchor dig in securely. Seasoned skippers often up-anchor early when a southerly builds, trusting experience more than forecasts.
Fishing and diving
Snapper may be scarce, but the harbour offers plenty to keep rods bending. Blue cod patrol the outer reefs, while summer schools of kahawai erupt on the surface, often signalled by wheeling flocks of birds. Butterfish, moki, tarakihi, and rig sharks round out a rich mix of species.
Fishing regulations are tight — including the 33 cm minimum size and two-per-person daily limit for blue cod, plus seasonal closures during spawning — and must be respected if these fisheries are to endure.
Divers and snorkellers enjoy plenty here too. Ocean Bay is renowned for its crayfish, while kina, pāua, and butterfish reward freedivers.
Ashore
The shorelines of Port Underwood are dotted with stories and small diversions. Ngakuta Bay holds the Ironside Cairn, a memorial to Reverend Samuel Ironside and the first Methodist mission of 1840.
South of Port Underwood, Whites Bay is prized for swimming and history — the site of New Zealand’s first telegraph cable in 1866. Robin Hood Bay, also south, offers surf and a DOC campsite. To the north, Walker Rock marks the Cook Strait cable protection zone, its sandy beach and sheltered waters drawing kayakers.
Simple pleasures abound too: strolling the beaches, picnicking, snorkelling in clear shallows, or exploring by dinghy. Together, they add another layer to the experience of this tucked-away harbour.
A tucked-away harbour worth the effort
Port Underwood blends history, diving, fishing, and anchoring in a way that sets it apart from the wider Marlborough Sounds. For those willing to sail from Picton or Waikawa, or to take on the gravel roads, the rewards are worth it: secure anchorages, good fishing, rich diving, and quiet DOC campsites.
Pack extra chain, plan your anchorage carefully, and keep a weather eye on the southerly. Whether exploring the Blackball wreck, or exploring the coastline by dinghy, Port Underwood offers a rugged, intimate alternative to the polished waters of Queen Charlotte and Pelorus Sounds — a tucked-away harbour with character all of its own.
