Green Island sits only a few dozen metres off the mainland south of Gap Beach in Hat Head National Park, close enough to touch by eye from the beach yet effectively impossible to reach except by dive boat because of the surf and rock in between. That short boat hop delivers one of South West Rocks' most consistently good second dives: a low reef encircling the island that starts gentle on its northern and eastern faces, around fourteen to seventeen metres over sand-fringed rock, and steepens dramatically on the south-eastern corner into a near-vertical wall cut with narrow gutters and overhangs. The site can be dived as a full loop of the island or as a drift, usually run north to south with the boat picking divers up at the southern end once the reef and current dictate the direction.

Green Island's status as a declared grey nurse shark critical habitat since December 2002 is the main reason for its popularity: in winter and spring aggregations of twenty, and on exceptional days as many as fifty, sharks have been recorded holding in the deeper gutters and along the wall, a scale that rivals Fish Rock itself despite the island's much lower profile among visiting divers. Away from the sharks, the reef supports a broad mix of temperate and subtropical fish — fiddler and eagle rays, resident loggerhead and green turtles, and large schools of drummer, bream, yellowtail and morwong — and the island has also had documented sightings of migrating humpback whales, including a mother with two calves, passing close by during the winter migration. Because the average depth is shallow and the site is well sheltered compared with the exposed outer reefs, Green Island is regularly used as an easier, confidence-building second dive on a South West Rocks trip, and works well for divers not yet ready for Fish Rock's currents and depths but wanting a genuine chance at a big grey nurse shark aggregation.

Boat access from South West Rocks, departing the town boat ramp/marina with Fish Rock Dive Centre or South West Rocks Dive Centre. The run is short — generally 10-20 minutes — as these sites lie closer inshore than Fish Rock itself, off Smoky Cape or between the town and Hat Head National Park. Boats moor or hold-station over the site for a direct descent; no surface swim required.

Sheltered relative to Fish Rock, but still exposed to easterly swell — best on light winds and under 1.5 m swell. Visibility affected by runoff after heavy rain. Winter and spring bring the largest grey nurse shark aggregations.

Descend the mooring near the island and follow the low reef east then south around the island's perimeter, or plan a drift from north to south (or the reverse) depending on the day's current, finishing along the steeper south-eastern wall where the reef becomes sheer with narrow gutters and overhangs.

Fish Rock Dive Centre (South West Rocks) — regular boat trips; South West Rocks Dive Centre — daily boat trips.