Cod Rock adds a distinctive geological feature to Broughton Island's dive roster: a lava tube swim-through, a reminder of the island's volcanic origins, running through a reef otherwise characterised by typical gutters and crevices in a depth range of twelve to eighteen metres. The tube gives the site a genuine sense of exploration beyond straightforward reef-hopping, and as the name suggests, cod are a notable resident, using both the tube and the surrounding crevices for shelter alongside the general mix of reef fish and invertebrates typical of Broughton Island's less current-swept, more sheltered corners. Compared with the island's headline grey nurse shark sites, Cod Rock is a lower-key, more purely scenic dive, well suited to a second or third dive on a Broughton Island day when the main shark encounter has already been had and a change of pace — structure and topography over megafauna — is welcome.

The lava tube itself requires reasonable buoyancy control and a torch to appreciate fully, since the interior is naturally darker than the open reef, but it does not demand technical cave training given its size and straightforward through-passage. This is a good site for divers who enjoy geological features and swim-throughs as much as fish life, and it rounds out a well-varied Broughton Island itinerary alongside the more famous Looking Glass and Shark Gutters. Local guides rate it as one of the more interesting structural dives on the island precisely because so few other NSW sites offer a genuine lava tube to swim through.

Boats depart Nelson Bay marina and run approximately 20 km/45-60 minutes north-east to Broughton Island, weather and vessel dependent. There is no facility or dive shop on the island itself; all diving is via day-trip charter from Nelson Bay, typically with two dives per trip around the island's northern and western sides depending on conditions.

Broughton Island sits fully exposed to ocean swell and is the first site cancelled when an easterly or north-easterly blow picks up; operators want well under 1.5 m swell and moderate wind to make the run worthwhile. The island's north side, where the grey nurse shark critical habitat sites (Looking Glass, Shark Gutters, North Rock) are found, gets some lee from a southerly, while other sides suit other wind directions, so skippers choose the exact site on the day. Visibility is best in autumn and winter, typically 10-25 m, and drops after rain from the mainland catchments.

Surge is common in the shallower features like Looking Glass and needs to be managed as a group.

Descend onto the reef and work through its gutters and crevices at 12-18 m, seeking out the lava tube swim-through as the highlight feature, checking for cod and other reef fish sheltering in the tube and surrounding rock before returning to the mooring.

Let's Go Adventures (Nelson Bay) and Feet First Dive (Nelson Bay) both run daily boat trips to Broughton Island, weather permitting.