Mercury Islands (Coromandel Peninsula)

For most divers the sweet spot is January to March, when sea temperatures hover near 20°C and settled high pressure systems often bring 10 m to 20 m visibility. December and April can also be excellent, but fronts are a little more frequent. Winter sometimes offers spectacular clear days, however water drops toward 15°C and you will need thicker suits and more flexible timing to catch the right window. If a particular advanced site is on your wishlist, plan at least a few possible dive days to allow for weather.

Fly into Auckland Airport (AKL), pick up a rental car, then drive roughly 195 km to Whitianga via State Highway 1, 2 and 25, allowing 2.5-3 hours in normal traffic. From Whitianga, you join a dive or scenic charter to reach Ahuahu and the wider Mercs, typically a 45-75 minute boat ride depending on weather and destination. There are no scheduled public ferries, and the smaller islands are DOC nature reserves with no public landing, so independent sailors must carefully follow Caulerpa and biosecurity rules.

Most local divers use at least a 5mm full suit year round, often stepping up to 7mm or a semi dry with hood and gloves from late autumn to spring. Summer sea temperatures peak around 20°C, which is comfortable with a 5mm and hood for two dives, while winter temperatures drop toward 15°C and make a thicker suit or drysuit very appealing. Freedivers typically use two piece open cell suits with integrated hood. If you run cold, err on the warmer side; it is easier to flush a suit than to warm up once chilled on the boat.

Yes, but only on the right sites and with the right operator. Sheltered bays like the inner parts of Coralie Bay and Peach Grove offer gradual depth, kelp gardens and sand channels ideal for Open Water training dives. However, many Mercs highlights are exposed to current and swell and are best reserved for Advanced Open Water divers with experience in cold water. When booking, be honest about your certification and recent dives so operators can pick appropriate locations or suggest closer inshore alternatives if offshore conditions are marginal.

Public landing is only routinely allowed on Ahuahu/Great Mercury Island and even there strict biosecurity and fire rules apply, with some areas remaining private. The other six islands are DOC nature reserves and are officially no landing to protect seabirds and other wildlife; camping is not permitted. Overnight access is generally limited to research and conservation teams with permits. Yachties sometimes anchor off approved Ahuahu bays, but should always check current rules, Caulerpa Controlled Area boundaries and any rahui or seasonal closures before planning a stay.

A Controlled Area Notice (CAN) for exotic Caulerpa covers waters around Great Mercury Island. Inside this zone you cannot remove any sea organisms, including fish, crayfish, shellfish or seaweed, and you must thoroughly clean anchors, chains and any gear that has contacted the seabed before leaving. For divers this means no spearfishing, no collecting and extra time rinsing, scrubbing and drying kit between sites. Most charter operators will brief you on the rules and may provide washdown facilities, but private boats must take full responsibility for compliance.

Non divers are spoiled for choice. Within a short drive you have Cathedral Cove and the Te Whanganui a Hei Marine Reserve for walking and snorkelling, Hot Water Beach for geothermal hot pools in the sand and surf, and the Mercury Bay Museum for history and culture. Inland, Coromandel Forest Park offers river walks and waterfalls. Scenic flights and boat cruises around Ahuahu provide a way to see the islands without getting wet. In peak summer, book popular activities and shuttles in advance.

Serious dive injuries from the Mercs are typically managed through the Diver Emergency Service (DES) and DAN in coordination with St John Ambulance and Coastguard. Initial care will occur in local medical facilities in the Coromandel and Waikato, but definitive hyperbaric treatment is usually provided at the Slark Hyperbaric Unit in Auckland, associated with Auckland City Hospital. In any suspected case of decompression illness, call DES on 0800 4 337 111 and 111 for emergency services, keep the diver on oxygen if available and follow medical advice while evacuation is arranged.

Standard travel insurance is a start but is rarely enough on its own. To dive or freedive the Mercs you should carry a policy that explicitly covers scuba and freediving to your planned depths, includes cold water and boat based activities, and provides for hyperbaric treatment and evacuation to Auckland if needed. Dedicated dive accident cover from providers like DAN or equivalent is strongly recommended. Check policy fine print for exclusions around pre existing conditions, technical dives and professional instruction if you plan to guide or teach.