Red Flag is one of a string of little-visited reefs along the cliff line between Maroubra and Malabar that only opened to divers after September 1990, when the Malabar sewage treatment plant's deepwater outfall took the effluent four kilometres offshore and the coast recovered. The site sits under the sheer cliff behind the centre of the Long Bay Rifle Range, marked by the small bay and the red warning flag that flies when the range is in use. Below the cliff a very small rock platform drops into 7 m of water and the reef edge is made of large rocks, some of them forming tunnels and caves that extend back under the platform.

Out from the shallows the bottom steps down through a 16 m reef to sand at 23 m. It is not a big site but the structure is interesting and the fish life is excellent: red morwong line the bottom, and the water column holds heaps of yellowtail, seapike and one-spot pullers, with good numbers of bream and small snapper. Wobbegongs and Port Jackson sharks visit seasonally, and one September dive found hundreds of Port Jacksons spread across the sand.

McFadyen notes the slimy weed that once covered the area in the outfall days has gone and the sponges have come back. Like its neighbours Tyre Reef, Rifle Range Reef and Yellow Rock it is a private-boat site; the charter operators run past it to Magic Point. That makes it a quiet, uncrowded intermediate dive for boat-owning divers from Botany Bay who want caves and fish without company, best done in the morning before the north-easterly.

Private boat only. Launch in Botany Bay (Cooks River/Kyeemagh or Foreshore Road), run out past Cape Banks and turn north; pass Little Bay, Long Bay and the Malabar wreck and run in towards the cliff behind the rifle range where a red flag flies when shooting is in progress – about 5 km and 20 minutes from the heads. Run north along the cliff until the sounder comes up from 23 m to 18 m or less and anchor.

No charter operator visits this stretch.

An open-coast cliff-base site with no shelter from east or south swell; the tunnels and caves under the platform become surge tubes in anything over about 1 m, and calm weather is needed to explore the shallow wall. Diveable in westerly and north-westerly winds; north-easterly sea breezes above 15 knots make the anchorage uncomfortable by early afternoon, so dive in the morning. The cliff top is an active rifle range – the red flag means shooting is in progress; the range fires out to sea and boats should stay in the designated safe zone.

Water quality improved dramatically after the 1990 Malabar deepwater outfall; visibility is typically 10–20 m.

From the anchor at 18 m swim east along the reef edge examining the large rocks and the tunnels that run back under the rock platform, then come back shallower over the 12–16 m reef towards the anchor, finishing in the caves near the platform if the swell allows. A 40-minute multilevel dive.

No regular charter – private boat or dive-club (St George Scuba Club) only