Poor Knights Islands

Every dive is a day-boat dive. Charters leave Tutukaka marina in the morning, cross to the islands in under an hour, and fit two dives around a surface interval spent anchored in a bay. Nobody goes ashore: the islands are a nature reserve and landing needs a permit recreational visitors do not get, so the boat is your only platform for the day. Skippers pick sites off the morning's wind and swell, and with so many bays and faces to choose from there is usually a sheltered option somewhere.

The islands drop straight into deep water rather than shelving off, so the diving happens close against vertical rock. What makes the terrain unusual is how comprehensively it is drilled through, with tunnels and archways piercing whole headlands and caves running back into the cliffs, at least one of them holding an air-filled chamber above the waterline. Kelp covers the shallow rock, sponge and gorgonian growth takes over further down, and there is no reef-building coral in any of it.

Fish density is the reason divers come back. In the gaps the schools stack up densely enough to close off the view of the far wall, and decades of protection have left the resident fish large and largely indifferent to divers. Conditions vary more than the photographs suggest: current runs hardest through exactly the gaps where the fish sit, surge inside the arches can push you around on a swelly day, and visibility can swing widely within a single dive as the current turns.

Trips tend to be short, since everything runs on the boat's schedule and two or three days covers the well-known sites without repeating them. Two decommissioned navy vessels were scuttled closer inshore off Tutukaka around the turn of the 2000s and are dived on separate charters, which is a useful fallback when swell shuts the outer islands down, though one of the two has broken up substantially in the storms since.