The Big Tāhuna

Snow-dusted mountain ranges rise across the wide horizon of Tasman Bay as swimmers wade into the waters off Tahunanui Beach. The Big Tāhuna is an open water swimming event staged in the sea at Tahunanui Beach in Nelson. Organized by the Ocean Swim Series, the race takes place in November, offering late-spring ocean competition. The event provides a tiered progression of distances to suit different ambitions, starting with 100-metre and 200-metre sprints alongside the 500-metre Mini Tāhuna. Swimmers seeking longer distances can step up to the 1.3-kilometre Small Tāhuna or take on the flagship 3.2-kilometre Big Tāhuna course across the bay. For those spending time in the region, the calendar allows pairing this swim with Opening Splash 2025, held three kilometres away just six days earlier.

Stepping into Tasman Bay in November delivers brisk conditions, with past editions recording water temperatures around 15 degrees Celsius. During the 3.2-kilometre race, swimmers have contended with long, rolling swells that obscure the course markers and demand focused sighting between wave crests. The effort is rewarded by expansive views stretching across the bay to distant alpine summits. Once dry, competitors gather in central Nelson at The Vic Public House for an after-party tradition linked to local lore, where two ocean swimmers first met in 2020 before later marrying.

Tahunanui Beach: the great sandbank and coastal rockpools

Tahunanui Beach frames the bay and defines the swimming arena from the shore out into deeper water. The beach extends across a 1.75-kilometre sweep of sand that shifts dramatically with the tidal cycle. At the eastern end, the receding low tide lays bare a network of rocky pools that shelter small shore crabs, fish, and sea snails. The coastal terrain here was altered by historic movement: the Tāhunanui slump of 1892 and the subsequent building of Rocks Road provoked coastal erosion that reshaped the beachfront over the decades that followed.

Nelson Haven and the 13-kilometre Boulder Bank

The entrance to Nelson harbour is protected by the Boulder Bank, a 13-kilometre natural spit composed of granodiorite boulders. These stones originate at Mackay Bluff, drifting at an estimated speed of 7.5 metres each year. Atop this stony ridge sits the Boulder Bank Lighthouse, erected in 1862 as the second permanent lighthouse constructed in New Zealand. To accommodate maritime traffic, an artificial passage was excavated through the stone barrier starting in 1903, reaching a width of 61 metres by 1905 and opening to larger vessels in 1906. Known as The Cut, this channel is maintained today at a width of 150 metres and is dredged every six months to sustain a draft of 10 metres.

Behind the barrier lies Nelson Haven, an estuary of salt marsh and mudflats spanning over eight kilometres long and up to two kilometres wide. The haven floods and empties with each tidal cycle, creating vast mudflats that support dense colonies of mud crabs. At the mouth of the Maitai River, the river estuary provides habitat for shorebirds such as the Red Knot and oystercatchers, while native fish including inanga and longfin eel share the fresh current with brown trout.

Fifeshire Rock and Haulashore Island: wrecks at the harbour gates

The opening of The Cut created the isolated 0.5-hectare plot known as Haulashore Island. During the 1960s, ferrets were introduced to this pocket of land in an effort to control its rabbit population. Only a narrow waterway separates Haulashore Island from Arrow Rock, a jagged islet sitting in Tasman Bay. Arrow Rock takes its name from the 212-ton brig Arrow, the first vessel to sail into Nelson harbour on November 2, 1841. The crag proved hazardous to early navigation, causing the shipwreck of the Fifeshire in 1842, after which the stone was renamed Fifeshire Rock. In September 1866, the schooner Three Sisters also wrecked after colliding with the rock. Today, the sea stack provides quiet roosting territory for spotted shags overlooking the bay.

Waimea Inlet and Rabbit Island: the ancient estuarine wilderness

About six kilometres away opens the Waimea Inlet, the largest estuary in the South Island, encompassing approximately 3,455 hectares. Formed over the last 6,000 years through post-glacial sea level rise and accumulated sediment, the inlet operates under significant tidal ranges between 2.6 and 4.2 metres. Although around 200 hectares of the original estuary have been lost to land reclamation since the 1840s, it remains an essential habitat for wading birds, including herons, egrets, spoonbills, and the banded rail. The inlet contains ten islands, of which Bell Island is the largest at 147 hectares. Another major landform within the estuary is Best Island, spanning 3.7 kilometres from northwest to southeast. While causeways link Best Island to the South Island and Bell Island, legal property access to its land parcels remains restricted to the water.

Sheltering the outer expanse of the estuary is Moturoa / Rabbit Island, which built up from barrier island deposits near the mouth of the Waimea River roughly 7,000 years ago. Māori occupied the barrier island for more than 800 years. In 1908, the Rabbit Island Recreation Reserve was formally established across Rabbit, Rough, and Bird Islands, preserving a wild coastal boundary.