Brennan Shoal is the northern neighbour of Roberts Shoal, off the Cape Moreton lighthouse, and the two are so alike that charter operators describe them together: similar terrain of pinnacles and big caves, generally calm currents but the potential for large swell. Depths run from about 12 m on the tops to 25 m around the base, with most of the dive spent between 15 and 20 m. The granite has been carved into pinnacles, overhangs and caves that shelter large wobbegong sharks, crayfish and moray eels, while schools of large pelagic fish – trevally, kingfish and mackerel – move around the shoal in the open water.

Sponges, soft corals and encrusting growth colour the rock. Visibility averages around 20 m. Brennan receives even fewer visits than Roberts, as operators heading for the cape tend to choose the better-known shoal or Smith Rock and Flinders Reef, so it is effectively a site for club trips and special outer-reef days.

That low traffic is part of its appeal: the fish are relaxed and there is rarely another boat in sight. Divers should come prepared for an exposed site with a long ride home and should be confident with navigation among caves and pinnacles, where it is easy to become disoriented. For divers who have explored Roberts Shoal, Brennan offers a similar experience with different caves and swim-throughs and a good chance of big fish.

Check marine park zoning before any private-boat visit, and treat conditions conservatively. Water temperatures range from about 19-21°C in winter to 24-27°C in summer.

Boat access only. Brisbane charters leave from Manly Boat Harbour (Brisbane Scuba departs from the corner of Royal Esplanade and Davenport Drive, Manly) or from Scarborough Boat Harbour on the Redcliffe Peninsula, crossing Moreton Bay and running out through the North West Channel past Bulwer and Comboyuro Point to the northern tip of Moreton Island. Allow roughly 75-90 minutes from Manly in good conditions.

Sunshine Coast operators run south from The Wharf, Mooloolaba, in about 45 minutes. Private boats typically launch at Scarborough or Bribie Island; the open-water crossing around Cape Moreton is exposed and should only be attempted in settled weather with local knowledge. Brennan Shoal lies just north of Roberts Shoal, east of Cape Moreton.

Like Roberts Shoal, currents are generally light but the site is fully exposed to ocean swell; easterly or south-easterly swell over about 1.5 m and strong winds rule it out. Best on calm winter days with westerly winds. Visibility averages about 20 m.

The ocean side around Cape Moreton can also carry a confused sea where swell wraps the headland, and summer afternoon north-easterly sea breezes make the return run uncomfortable, so trips leave early.

Descend onto the tops of the pinnacles, explore the caves and gutters at 15-20 m, check the sand edges for wobbegongs and look up for pelagic schools, then return to the anchor or ascend on a DSMB.

Supercat Charters and Brisbane operators – occasional outer-Moreton days in calm weather; no regular schedule.