The Aquarium earns its name honestly: tucked into the south-western corner of Fish Rock near the cave's shallow entrance, it is a compact, shallow reef packed with an unusually dense and varied fish population, making it one of the most relaxed and rewarding dives on the island for divers of any experience level. From the mooring, the route runs north-west along a boulder-lined gutter before climbing a slope to the Turtle Hole, a distinctive bowl-shaped depression about five metres across and ten metres deep, its floor littered with broken barnacle shells, which for many years was the territory of a long-resident and famously placid green turtle. The site's shallow average depth — much of it sits between ten and twenty metres — means bottom times of up to an hour are routine, a rarity at a location otherwise built around deeper walls and gutters.

Fish life is the drawcard: dense schools of silver sweep, yellowtail and ladder-finned pomfret hang over the reef, rainbow runners cut through the open water, and the rockier margins hold white-eyed moray eels, banded coral shrimp, nudibranchs, Spanish dancers and juvenile boxfish in the cracks. Wobbegongs and grey nurse sharks both pass through the Aquarium's fringes, clownfish and anemones occupy a shallow patch reef, and green turtles are reliably encountered resting or feeding. Because it sits right beside the cave's shallow entrance, it is commonly dived as the back half of a cave dive or as a stand-alone second dive when the Pinnacle or Colorado Pass are running too much current to be workable.

Michael McFadyen, who has logged the site for decades, rates it among his favourite dives anywhere — a case of a site whose lack of drama (no big wall, no deep drop-off) is exactly what makes it such a satisfying, unhurried look at everything Fish Rock does well in miniature.

All Fish Rock sites are boat access only, departing from the boat ramp/marina at South West Rocks (Fish Rock Dive Centre and South West Rocks Dive Centre both operate from the town, 4 New Entrance Road area). The run out to Fish Rock, off Smoky Cape about 2 km offshore, takes roughly 15-25 minutes depending on the vessel and sea state. Boats moor directly on the site — there is a southern mooring near the cave/shark gutters and a northern mooring near The Pinnacle — so there is no surface swim; divers descend the mooring line straight onto the reef.

Double boat dive trips (two dives, roughly 5 hours total) run most days when weather allows; book ahead as Fish Rock is a signature Australian dive and trips fill, especially in the May-November grey nurse season.

Fish Rock sits in open ocean off Smoky Cape with no shelter, so trips are cancelled on any strong onshore swell or wind over about 20 knots; operators want under 1.5-2 m swell to run safely. The site is affected by a north-setting current for roughly 80% of the time, and it can run strong enough to make the cave and Pinnacle undiveable — the best conditions are the day after the current has dropped out or during a brief slack. Visibility is usually 15-30 m and can be exceptional (30-40 m) inside the cave itself; it drops after east coast lows and heavy rain runoff from the Macleay River.

Grey nurse sharks are present year-round but peak May-September, with leopard (zebra) sharks more likely February-April. Dived year-round; winter mornings before the sea breeze are usually calmest.

Descend the mooring and head north-west along the main gutter over boulders, then up a slope to the east toward the Turtle Hole, a five-metre-wide bowl at about 10 m. Loop south and east across rocky bottom, watching for resident turtles and moray eels, then return via the main gutter to the mooring, using the shallow depth to extend bottom time to around an hour.

Fish Rock Dive Centre (South West Rocks) — double boat dives most days, year-round; South West Rocks Dive Centre — daily boat trips to Fish Rock.