Safety · Destination Guide
Wild kelp forests and predator free islands off the Coromandel coast
Updated Nov 21, 2025 • 9 sources
The Mercs combine remote feeling offshore conditions with strong conservation protections. Safety revolves around respecting cold water and open sea conditions, planning conservative dives and having clear emergency plans, while conservation centres on keeping the islands pest free and slowing the spread of exotic Caulerpa.
Treat Mercs dives as offshore, cold water dives even when the forecast looks benign. Use appropriate exposure protection, carry SMBs on every team, plan gas and turn pressures conservatively and adjust for the extra effort of swimming in current and surge. Many sites are a considerable distance from sheltered anchorages; be ready for imprecise drop offs and blue water ascents. Agree clear recall and separation procedures with your skipper, including what to do if you surface far from the boat. Always dive with a competent buddy and follow recognised training agency limits for depth, no decompression time and overhead environments. For advanced sites like Never Fail Rock, dive only with skippers who know the area well and are comfortable saying no when conditions are marginal.
The nearest major medical facilities are on the Coromandel Peninsula and in the Waikato region, with advanced hyperbaric services based in Auckland (Slark Hyperbaric Unit and Auckland City Hospital). In case of a suspected dive injury, activate the Diver Emergency Service (DES) via 0800 4 337 111, contact DAN if you are a member and call 111 for ambulance or coordinated rescue. Whitianga has medical practices and ambulance services, but serious cases will usually be transported to larger centres. Maritime emergencies should also be raised on VHF Channel 16 with Maritime Radio and Coastguard.
Caulerpa Controlled Area - no take and strict cleaning
Great Mercury Island sits inside a Controlled Area Notice aimed at stopping the spread of exotic Caulerpa seaweed. You cannot take any marine life, including fish, crayfish, shellfish or seaweed, from the zone, and you must thoroughly clean anchors, chains and any gear that has contacted the seabed before leaving. These rules apply year round and breaking them can result in heavy penalties.
No landing on DOC nature reserve islands
All Mercury Islands except Ahuahu/Great Mercury are DOC administered nature reserves with strict no landing rules to protect vulnerable wildlife. You may anchor offshore within relevant Caulerpa and fishing rules, but setting foot on shore without a permit is illegal. Report any suspected illegal landings to DOC.
Exposed seas and fast changing weather
The Mercs sit in open water and are exposed to swell and wind from most directions. Even with good forecasts, conditions can deteriorate quickly, especially when fronts or tropical remnants sweep across the upper North Island. Expect rough rides, be prepared for trips to be cut short or switched to inshore sites, and carry adequate seasickness medication if you are prone.
Cold water and long surface intervals
Even at summer peaks, water temperatures are much cooler than tropical destinations, and winter dives can feel brutal without proper insulation. Plan for long boat rides and surface intervals exposed to wind; bring extra layers, windproof jackets, beanies and hot drinks to avoid getting chilled between dives.
Conservation at the Mercs operates on two fronts: land and sea. On land, six of the seven islands are DOC nature reserves and all but Ahuahu are strictly no landing to protect globally significant seabird and reptile assemblages. Great Mercury has undergone major pest eradication and ecological restoration, and visitors must comply with strict biosecurity and fire rules. At sea, the Caulerpa Controlled Area at Ahuahu bans taking any marine life and imposes stringent cleaning requirements on anchors and gear to prevent spread of invasive seaweed. Divers, freedivers and snorkellers should maintain impeccable buoyancy control, avoid touching reefs, never feed fish and decontaminate equipment between regions. Respect any rahui or community led closures that may apply.
Do Not Do This
Avoid entering when caulerpa controlled area - no take and strict cleaning. Confirm local briefings before committing.
| Contact | Role | Phone | Availability |
|---|---|---|---|
| New Zealand emergency services | Police, Fire, Ambulance and Search and Rescue coordination | 111 | 24/7 nationwide, free from any phone in New Zealand. |
| Diver Emergency Service (DES) / Dive Emergency Number | Diving and hyperbaric medical advice and coordination | 0800 4 337 111 | 24/7 hotline for all dive related emergencies in New Zealand. |
| Coastguard and Maritime Radio (VHF 16) | On water emergencies, vessel assistance and coordination with other services | VHF Channel 16 (call "Coastguard" or "Maritime Radio") | Continuous monitoring around the New Zealand coast; used alongside 111 for serious incidents at sea. |
| DAN World emergency hotline | International dive emergency support for DAN members | +1-919-684-9111 (global English line) | 24/7 worldwide dive emergency assistance hotline. |