Cat Reef lies alongside Tijou Reef on the far-northern shelf edge, and Mike Ball's Northern Exposure expeditions dive the two together: wall dives adorned with colourful fans and soft corals, with barracuda, rays, sharks and turtles and pelagic activity. Scuba Diver Life lists Tijou, Cat, Great Detached and Small Detached reefs as key sites of the Raine Island expedition. The reef's outer face drops steeply into deep water, with gorgonian fans, whip corals and soft corals on the walls and hard corals on the upper slopes.

Currents bring pelagic fish – barracuda, trevally, mackerel – and sharks patrol the walls. Turtles are common, especially during the nesting season when thousands head for Raine Island to the north. Named sites on the Tijou/Cat system include Pussy Galore and Catchers Mitt (listed separately); it is not always clear from operator notes which of the two reefs each lies on.

The site is visited only on expedition liveaboards, a few times a year, and requires Advanced certification or equivalent. Visibility is typically excellent. Cat Reef suits experienced divers on a far-northern expedition who enjoy wall diving and pelagic encounters.

Getting here is itself an expedition: the far-northern reefs lie hundreds of kilometres north of Cairns, are visited by only a handful of liveaboards in the October–December window, and are many hours from medical help, so divers should be current, self-sufficient, carry an SMB and audible signal, and dive conservatively. On Mike Ball's Northern Exposure itineraries the Tijou and Cat reefs are dived over a day of the seven-night voyage between Cairns and Horn Island, typically with up to four dives including a night dive, and the exact sites chosen depend on the weather on the day.

Liveaboard only – there are no day boats, resorts or public moorings this far north. Mike Ball Dive Expeditions' Spoilsport runs 7-night 'Northern Exposure' expeditions between Cairns (Trinity Wharf) and Horn Island in the Torres Strait each November (northbound and southbound, up to 27 dives), plus a 7-night Far North Coral Sea Exploratory round trip from Cairns in October. Spirit of Freedom runs 7-night far-north expeditions from Cairns in October–December, and Professional Dive Services' MV Kalinda has run longer (13-night) Cairns–Horn Island trips.

Horn Island has daily scheduled flights to Cairns (book separately; allow 24 hours after diving before flying). The far-northern reefs are roughly 500–650 km north of Cairns – one to two days' steaming each way.

The far-northern reefs are only diveable in a narrow weather window. The south-east trades blow hard from about April to September and make the long open-water passage and the exposed outer walls impractical, so expeditions run in the transition period, typically October–December, when winds are lighter; the northerly monsoon, storms and cyclones (December–April) close the season. Even in the window, exposed shelf-edge walls (Tijou, Great Detached, Raine) need calm days, and skippers switch between reefs to find shelter.

Strong tidal currents and upwellings run along the continental shelf and through reef openings – channel sites are timed to slack water. Visibility varies from about 12 m to 40 m+ depending on tides and any rain. Marine stingers are present from November.

Drop onto the wall at 18–22 m and drift with the current, then rise onto the reef top or into the gullies for the safety stop and tender pick-up.

Liveaboard only: Mike Ball Dive Expeditions (Spoilsport – 7-night Northern Exposure Cairns↔Horn Island, November; 7-night Far North Coral Sea Exploratory, October); Spirit of Freedom (7-night far-north expeditions, October–December); Professional Dive Services MV Kalinda (occasional long expeditions). Requirements typically Advanced certification or 15+ logged ocean dives.