Masthead Island is an undeveloped national park cay in the Capricorn Group, west of Heron Island and about 60 km from Gladstone. It is surrounded by a closed lagoon and reef system, supports Pisonia forest, and is a nesting site for seabirds (November-March) and shearwaters (October-May). Camping is permitted for small groups under QPWS permit, subject to seasonal closures.

The fringing reef edge offers healthy hard coral gardens with turtles, reef sharks and rays. What makes the area particularly interesting for divers is nearby Polmaise Reef, where the Polmaise Bommies offer overhangs and swim-throughs in 16-20 m, and the remains of the 1879 steamer Tambaroora lie in 8 m. Masthead sees very few divers because there is no operator; visitors are private boat owners, campers and occasional liveaboards touring the Capricorn Group.

That means the reef is quiet, but also that divers must be completely self-sufficient, carrying their own air, oxygen and communications. The island suits experienced divers with their own vessel who want to explore a less-visited part of the southern Great Barrier Reef, and camping groups with snorkelling in mind. Anyone visiting should respect the seabird nesting colonies and the closure periods.

Masthead can be combined with Heron (where the resort is for guests only), Erskine and Wilson islands and North West Island in a multi-day boat trip through the Capricorn Group. Because the lagoon is enclosed, anchoring inside is not possible for most vessels; plan to anchor off the reef in the lee and use a tender for landings and shallow snorkelling.

The Capricorn Group lies 60-100 km north-east of Gladstone. Private boats launch from Gladstone Marina (Bryan Jordan Drive; ramps, fuel and trailer parking) and cross the shipping approaches and open water, typically 2-4 hours depending on vessel and destination; the Capricorn Bunker liveaboards that occasionally visit depart Gladstone or Yeppoon (Rosslyn Bay) and anchor overnight in the lee of the cays. Camping on the national park cays requires a QPWS permit and a camper transfer or private vessel.

Masthead Island is about 60 km from Gladstone, roughly 2-3 hours by private boat. Camping is by QPWS permit (30-60 people, seasonal closures for nesting seabirds). Boats anchor in the lee of the reef; the Polmaise Bommies and Tambaroora wreck lie on nearby Polmaise Reef.

The Capricorn cays are exposed to the south-east trades (often 15-25 knots April-September), which make the Gladstone crossing rough and restrict diving to the lee (north-western) sides. The calmest windows are typically September-December and March-April. Northerlies in spring and summer reverse the sheltered sides.

Tidal currents run strongly around reef edges and channels on springs. Cyclone season November-April. Masthead's surrounding lagoon offers some shelter, but the reef edges are exposed to the trades; choose the lee side for diving.

Anchor in the lee of the reef, descend to the reef edge at 10-15 m and follow it along, looking for turtles and sharks, then return over the shallower coral for the safety stop. Combine with the Polmaise Bommies and the Tambaroora wreck nearby.

No daily operator. Occasional liveaboard itineraries (for example the 8-diver MV Adori run by Professional Dive Services, 4 days/3 nights from Yeppoon) and fishing/snorkel charters such as Eastern Voyager visit the Capricorn cays; otherwise private boats and camping groups only. MV Adori itineraries have included Masthead Island.