The Tambaroora was a 356-ton steamer that ran aground on Polmaise Reef, near Masthead Island, in 1879. Its remains lie in about 8 m of water on the reef, where more than a century of storms has broken the vessel down into scattered wreckage now largely overgrown by coral and algae. The Marine Life Network lists the site with visibility of about 10 m and a fish population that includes damselfish, bream, coral trout, sweetlips and pufferfish, with wobbegongs and tawny nurse sharks resting under the plates and bass sheltering in the structure.

The wreckage provides shelter on an otherwise flat reef area, which concentrates the fish. Because it is shallow, the wreck makes a relaxed dive or snorkel in calm weather and a good second dive after the nearby Polmaise Bommies. There is little recognisable structure left, so the interest lies in picking out pieces of machinery and hull among the coral and in the resident fish and sharks.

As a historic shipwreck more than 75 years old, the Tambaroora is protected under the Underwater Cultural Heritage Act 2018: nothing may be removed or disturbed. The site suits Open Water divers and snorkellers with access to a private boat, and it is one of several historic wrecks in the Capricorn Group, alongside the SS Cooma on North Reef. The shallow depth also gives long bottom times and bright natural light for photographing the coral growth that has turned the wreckage into a small reef of its own.

Watch for small blennies and gobies living in the corroded plates.

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.

The wreck lies on Polmaise Reef near Masthead Island at the published position -23.5733, 151.6808, roughly 2-3 hours by private boat from Gladstone. Anchor on sand off the reef and swim in to the wreckage.

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. The wreck is on the reef edge in shallow water, so surge makes it unpleasant in any swell; dive in calm conditions near high tide.

Descend onto the wreckage in 6-8 m and swim slowly around the scattered plates and machinery, looking under them for wobbegongs and tawny nurse sharks. Keep clear of the reef crest if any swell is running.

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.