Big Saigon is one of a pair of excellent wall dives off Cape Baily that were largely ignored for decades. In the past this stretch of coast was avoided because of the outfall from the Cronulla sewage treatment works and discharges from the Kurnell oil refinery; with deep-ocean outfalls and the refinery's closure as a refinery, water quality improved, and McFadyen's club began exploring it. The name comes from its sister site, Little Saigon, about 140 m to the south, which was named after the Vietnamese fishers regularly seen in the area.

The main feature is a wall running north–south with its top at about 17 m, dropping to 20 m in spots and then to about 25 m at the base, with deeper steps going past 32 m without reaching the sand edge. The wall is riddled with overhangs, small swim-throughs and arches, including a small archway right beside the usual anchorage. Away from the wall the reef is scattered with boulders, some small and some very large, and gullies formed by big boulders interrupt the wall's line.

McFadyen explored about 200 m north with a scooter and found the wall continuing with the same character. The encrusting life is excellent: sponges, sea squirts and small gorgonians cover the wall faces. Fish life is very prolific, with one-spot pullers, silver sweep, small seapike and yellowtail in schools and mosaic and six-spined leatherjackets among the rocks.

The site is very close to the Hilda wreck, which lies under 200 m off the lighthouse, and the two can be combined on a day out from Port Hacking. Big Saigon suits experienced Advanced or deep divers, ideally on nitrox, who want a wall dive with prolific life that sees very few other divers.

Boat only – the Kurnell cliffs are sheer and in Kamay Botany Bay National Park, with no practical shore entry. From Botany Bay, launch at Kyeemagh (Cooks River), Foreshore Road or Bonna Point (Silver Beach, Kurnell), run out past Captain Cook's Landing Place, Inscription Point and The Leap, then turn south along the cliffs; from Port Hacking (Gunnamatta Bay/Tonkin Park or Lilli Pilli ramps) run out past Bass and Flinders Point and north-east along Bate Bay past Cronulla Beach and Cape Baily. From Port Hacking this is the closest of the Kurnell sites – about 10–15 minutes out past Bass and Flinders Point and across Bate Bay to Cape Baily Lighthouse; from Botany Bay about 25 minutes south past Cape Solander.

McFadyen's GPS is 34° 02' 12.3" S 151° 13' 35.2" E on the older AUS66 datum (roughly 200 m shift to WGS84 – convert before use). Find the wall a very short distance to the east and anchor on the reef top at about 17 m, close to the small archway.

Cape Baily is one of the most exposed points on this coast, catching swell from the north-east through south; seas are often extremely rough and the site should only be dived with swell under about 1.5 m and light winds, ideally winter westerlies. The area was avoided for years because of outfalls from the Cronulla sewage treatment works and the former Kurnell oil refinery; water quality has since improved, but visibility still falls after rain. The East Australian Current can run along the cliffs.

Afternoon north-easterlies in summer make anchoring and recovery uncomfortable; go early.

From the anchor beside the small arch, drop over the wall and follow it north at 20–25 m through the overhangs, swim-throughs and boulder gullies, then return along the reef top at 17–20 m. The wall continues at least 200 m north; deeper sections past 32 m are for nitrox/deep divers only.

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