Middle Ground is one of the finest deep reefs off southern Sydney, and McFadyen calls it a brilliant site – with the caveat that unless you own a boat or belong to the St George Scuba Club, you cannot dive it. It lies straight out from the Port Hacking entrance, only minutes from the Cronulla ramps. There are two reef sections.

The main site is about 120 by 80 m, with a flat top at 28–29 m and a wall of up to 3 m on its southern and eastern edges dropping to sand at 31–33 m. A larger reef to the north-east covers about 200 by 150 m and is listed separately as Middle Ground North. The reef is cut by parallel north–south cracks and has overhangs, cracks and holes throughout, with a large, low cave on the eastern wall.

For its size the site carries remarkable life. Large schools of yellowtail, sweep, ladder-finned pomfret and seapike surround it; Port Jackson and wobbegong sharks rest under ledges; eastern blue devilfish and red morwong occupy the holes; and McFadyen has counted up to six giant cuttlefish on one dive. Wandering anemones, nudibranchs and sponges cover the reef, loggerhead turtles have been seen, and seals appear on about 60 percent of dives – one of the best seal encounters in Sydney.

Visibility is usually 10–15 m and occasionally 25–30 m. On air the no-decompression time is about 16–17 minutes, but because the reef is compact a full circuit takes only 10 minutes, so divers see the whole site on one dive. It suits deep-experienced divers, ideally on nitrox, who want a compact reef with reliably big animal encounters.

Boat only. Launch in Port Hacking at Tonkin Park/Gunnamatta Bay (Cronulla), Lilli Pilli or Grays Point and run out past Bass and Flinders Point and Oak Park into Bate Bay. Middle Ground is straight out of Port Hacking, about 10 minutes from the Cronulla ramps.

McFadyen's GPS is 34.07445° S 151.190929° E. Anchor on the reef top at 28–29 m. There is no longer any dive charter operating out of Port Hacking, so it is a private-boat or St George Scuba Club dive.

Bate Bay faces south-east and is open to swell from the east through to the south; southerly and south-easterly seas over about 1.5 m make the Bate Bay reefs rough and the Port Hacking bar can be dangerous in big swell. North-westerly and westerly winds give the calmest conditions; summer north-east sea breezes chop up the bay in the afternoon. After heavy rain, Port Hacking and the Cronulla stormwater drains discolour the inshore water.

At 28–33 m the reef is below most surge, but the boat ride and anchoring become difficult in southerly seas over about 1.5 m. Visibility is typically 10–15 m, sometimes 25–30 m on clean ocean water; runoff from Port Hacking after heavy rain reduces it. Current is usually light.

Descend to the reef top, follow the wall east until it turns north, continue north (past the large low cave on the eastern wall), then reverse. A full circuit of the main reef takes about 10 minutes, fitting within the 16–17 minute no-deco limit on air.

Nitrox (EAN28–30) recommended to extend the 16–17 min air no-deco limit.

No regular charter – private boat or dive-club (St George Scuba Club) only; no charter boat currently operates out of Port Hacking.