Admin Wall is the name Extra Divers use for the steep wall section of the Flying Fish Cove drop-off – the more dramatic, deeper half of the cove's shore diving, as opposed to the gentle Sandpatch. It shares the cove's entry, but the dive itself feels like a boat dive on the island's outer walls: the reef top at 5–10 m ends abruptly and the face drops away into deep blue water, with nothing below you but more wall. Extra Divers describe it as a sheer drop teeming with trevally, fusiliers and reef sharks.

The wall face is covered in hard corals near the lip – plates, boulders and encrusting forms – and sea fans, whips and soft corals as you descend. Crevices shelter squirrelfish, soldierfish, groupers and moray eels, while schools of fusiliers stream along the face. Out in the blue, giant and bluefin trevally hunt, whitetip and grey reef sharks patrol, and in the wet season whale sharks are regularly encountered cruising along the edge of the cove, having followed the red crab spawn. The endemic and hybrid reef fish that make the cove famous – Christmas Island (Cocos) angelfish and hybrid butterflyfish among them – are seen on the reef top.

Because the wall is effectively bottomless, Admin Wall rewards good buoyancy and depth discipline, and it is a natural next step for divers who have done the cove's shallower sections. It can be dived from shore with hired tanks, but many visitors dive it guided or as a short boat dive first to learn the layout. It is also the obvious place to watch for pelagics on a dusk dive. The wall and adjoining cove are the most heavily used water on the island, yet the coral remains in excellent condition, which says much about the health of Christmas Island's reefs and the small number of divers who visit.

Fly from Perth (about 4 hours, two to three flights a week, some via Cocos Islands) and hire a car – there is no public transport. Flying Fish Cove is the harbour at The Settlement, a two-minute drive from the dive shops and five minutes from most accommodation. Park in the beachside car park opposite the boat ramp at the western (southern) end of the cove, gear up at the car or picnic shelters, and walk straight down the concrete ramp into the water – a carry of only 20–30 m.

Alternatively step off the low water-level platform on the public jetty. Surface-swim or fin along the bottom 30–50 m over the inner reef flat to the drop-off. Tanks and weights can be hired from Extra Divers or Wet'n'Dry for independent dives.

Admin Wall is the steeper section of the drop-off; ask the dive shop to point out the exact line on a chart before an independent dive.

Flying Fish Cove faces north-west and is the most protected water on the island through the south-east trade season (roughly April/May–November), when it is diveable almost every day. In the wet season (December–March/April) north-westerly monsoon swell, and swell from distant cyclones, rolls straight into the cove – the beach then becomes a surf break, the entry over the reef flat is dangerous and boat launching can be suspended; Extra Divers treat February–April as peak swell season. Avoid entering when waves are breaking on the reef flat; low tide makes the inner reef very shallow (snorkel it at high tide).

Tides are small (about 1 m). Visibility drops after heavy rain run-off and during red crab spawning (October–January), when crabs release eggs into the cove before dawn and whale sharks are most often seen off the drop-off. Night dives are best on calm dry-season nights.

Descend to the drop-off and follow the wall with it on one shoulder at 18–25 m, looking out into the blue for trevally, reef sharks and whale sharks in season. Turn on one-third to half gas, ascend to the lip of the wall at about 9–10 m for the return and finish with a safety stop over the reef top before swimming back to the ramp.

Extra Divers Christmas Island – guided shore and boat dives on Admin Wall as part of Flying Fish Cove diving; CI Wet'n'Dry Adventures – dives the cove wall when conditions suit.