Trennents Rock is a reef a few hundred metres south of the Tollgate Islands. The Marine Life Network lists it at 7–25 m and highlights huge numbers of pelagic and reef fish, weedy sea dragons and kelp beds. Beyond that brief summary it is not well documented, but it shares the character of the Tollgate Islands reefs, with the added exposure of sitting a little further out into the bay.

The shallower parts of the reef are covered in kelp, which is where the weedy sea dragons live. They are best found by moving slowly and scanning just above the kelp canopy. Deeper, the reef breaks into boulders and ledges with sponges and sea squirts, and the reef edge attracts schools of yellowtail, sweep and bream, with kingfish, bonito and trevally passing through, particularly in summer. Blue groper, red morwong, wobbegongs and eastern blue devilfish are the usual reef residents, and grey nurse sharks from the nearby Dragon Rock colony may pass.

The site suits Open Water divers who stay on the shallow kelp and Advanced divers who want to explore the deeper edge. It is a good alternative to the island sites when they are busy or when divers want pelagic action. Coordinates here are approximate, estimated from the 'few hundred metres south of the Tollgate Islands' description. Check with a local operator for the exact mark, and treat the depth range as indicative. It is unclear whether the reef is inside the Tollgate Islands sanctuary zone, so check the zoning map before fishing.

Boat access only. Beneath the Bay leaves from the Hanging Rock ramp in Batemans Bay and runs out to the Tollgate Islands in the middle of the bay, about 10–15 minutes; private boats also use the ramps at Batehaven, Wimbie Beach and Mosquito Bay (Lilli Pilli). Landing on the islands (a nature reserve) is not permitted.

Trennents Rock is a few hundred metres south of the islands; locate it on the sounder and anchor on the reef.

South of the Tollgate Islands, Trennents Rock is more exposed to southerly swell than the sheltered island sites. Dive it on westerly or northerly days with swell under about 1.5 m. Strong summer north-easterlies make anchoring uncomfortable.

Visibility falls after heavy rain in the Clyde catchment.

Descend onto the reef, search the kelp beds for weedy sea dragons, then drop down the reef edge towards 20–25 m where the pelagic schools tend to gather. Return shallower along the kelp to the anchor.

Listed by the Marine Life Network as a Batemans Bay boat dive. Dived occasionally by local operators and visiting clubs; no scheduled trips published.