The Trench is one of the deeper, more exposed swim-through features on the south-eastern side of Julian Rocks, cutting through the rock in the same general area as Cray Cave and Gorgonian Hollow but forming its own distinct passage rather than the shallower, twin-channel Hugo's Trench found on the eastern side of the island. Depths run from about 12 m at the shallower end to 22 m where the trench opens toward the deeper reef, putting this dive a notch above the more sheltered Nursery and Hugo's Trench in both depth and typical current. As on the rest of this flank of Julian Rocks, the appeal here is a mix of dramatic swim-through topography and a genuine chance of grey nurse sharks through the cooler months, when the animals use the trench's walls to shelter from current in much the same way they use the nearby Cray Cave and Cod Hole.

Wobbegong sharks lie along the trench floor, turtles pass through routinely, and the trench walls themselves support a good covering of sponges, gorgonians and small invertebrate life for divers who take the time to look closely rather than simply transit through. Because The Trench sits on the more exposed side of the island, it shares the same weather sensitivity as Cray Cave and the Cod Hole: a moderate south-easterly swell will generate enough surge inside the passage to make it unpleasant or unsafe, and operators will substitute the sheltered Nursery or Hugo's Trench on those days. On a calm day with reasonable visibility, though, this is one of the more satisfying deeper swim-throughs at Julian Rocks, offering genuine canyon-style diving without needing to leave the shelter of the island's own reef system.

Divers should have solid buoyancy control given the narrower sections and the depth involved.

Both Byron Bay dive operators launch small rigid-hull inflatables directly off the beach: Sundive Byron Bay from The Pass, Byron Bay Dive Centre from near Wategos/Clarkes Beach; check in first at the shopfront in town, then walk down to the beach for the boat launch briefing.

Julian Rocks sits fully exposed 2.5 km off Byron Bay; a big easterly or south-easterly swell closes the outer sites but the Nursery side can often still run. Visibility can change from 5 m to 20 m within a single day as warm and cool currents meet around the rocks. Summer (Dec-Mar, 21-26°C) brings leopard sharks and mantas; winter (Jun-Aug, 18-21°C) is cooler but usually clearer, with grey nurse sharks and migrating humpback whales.

Enter the trench near its shallower northern end at 12-14 m, follow the walls down to 20-22 m watching for resting grey nurse sharks and wobbegongs, and exit at the deeper southern end toward Cray Cave before ascending along the outer wall.

Sundive Byron Bay (The Pass) and Byron Bay Dive Centre (Wategos/Jonson St) both run daily boat dives to Julian Rocks.