The Cod Hole is the dive that put the Ribbon Reefs on the world map. It lies at the very northern tip of Ribbon Reef No. 10, where the long outer barrier breaks up into a series of coral ridges and sand gutters facing Cormorant Pass. The star attraction is a resident group of potato cod (Epinephelus tukula), the second-largest grouper in the Indo-Pacific, which can reach two metres and 100 kg. Operators report anywhere from one to eight fish on a dive. Decades of controlled feeding under permit have made them remarkably relaxed with divers, and they cruise within centimetres of a mask, following people across the sand like large, curious dogs.

The site itself is more varied than its reputation suggests. Below the mooring is a sandy arena at 12–15 m bordered by long coral ridges that guides call the 'Supermarket Aisles'. The reef was badly damaged by Cyclones Yasi (2011), Ita (2014) and Nathan (2015), but by the 2020s Mike Ball's guides were describing new Acropora colonies everywhere on the shallow ridges and healthy growth on the eastern side. Deeper, the terrain drops to about 30 m, where gorgonian fans host pygmy seahorses. There are caverns and swim-throughs, a section known as Shark Alley for its whitetips, and a lagoon side worth exploring on a second dive.

Beyond the cod, the Cod Hole is a genuine big-fish site. Queensland groupers gather in the deeper sections in spring and summer, flowery and camouflage groupers are common, and diagonal-banded sweetlips can form aggregations of several thousand in spring. Schools of bumphead parrotfish, red bass, sailfin snapper, grey and whitetip reef sharks, lacy scorpionfish and anemonefish round out the list, and whale sharks, manta rays and great hammerheads turn up occasionally. It suits every level of diver; the shallow sand arena makes it an easy dive, while the ridges and deeper fans keep experienced divers and photographers busy.

Liveaboard only (or fly-dive via Lizard Island). Mike Ball Dive Expeditions' Spoilsport and Spirit of Freedom depart Cairns (Trinity Wharf / Marlin Marina) in the evening and steam north overnight, roughly 12–14 hours and 200–250 km, to reach the Ribbon Reefs by morning; some itineraries fly Cairns–Lizard Island (about one hour, scenic flight along the coast) and board or disembark there. Trips run 3–7 nights and include the Cod Hole on almost every Ribbon Reef itinerary.

Divers enter by giant stride from the dive deck at the mooring and descend the mooring line. Lizard Island Resort also runs day dives to the Cod Hole (about 50 minutes each way) for resort guests. There are permanent moorings at the site; boats tie up on the sheltered side and divers drop straight onto the terraced reef below.

The Ribbon Reefs sit on the edge of the continental shelf and take the full south-east trade wind from April to October. Lagoon-side moorings stay diveable in 20–25 knot SE winds, but reef-front sites and passes need lighter winds; liveaboards shelter behind the reefs overnight. September to December is usually calmest.

Tidal flow through the gaps between the Ribbons is strong on springs, so exposed pinnacles are timed for slack water. December to April brings rain, lower visibility and cyclone risk; box jellyfish and Irukandji are possible November to May. The Cod Hole mooring is on the lee of the reef tip and is one of the most reliably diveable sites on the Ribbons, but the incoming tide can push a noticeable current across the ridges.

Descend the mooring to the sand arena at about 12–15 m where the potato cod gather. Settle on the sand as briefed and let the cod approach; keep hands tucked in. Afterwards explore the coral ridges ('Supermarket Aisles') and the deeper fans toward 30 m if gas allows, then work back up the ridges into the shallows for the safety stop at 5 m over the reef top.

Mike Ball Dive Expeditions (Spoilsport) – Ribbon Reef, Cod Hole and Coral Sea itineraries from Cairns, several departures a month; Spirit of Freedom – 3-, 4- and 7-night trips from Cairns/Lizard Island, weekly; Lizard Island Resort dive shop – day trips for resort guests (about 50 min).