Hugo's Trench takes its name from the pair of parallel fissures that run through the eastern flank of Julian Rocks, their sheer rock walls close enough together in places that divers pass through what feels like a canyon rather than open reef. Depths run from about 8 m at the top of the trenches to 18 m where they open out, and because the walls provide some shelter from swell and current this is often the site of choice when the fully exposed Cod Hole is too rough to dive safely, making it one of the more consistently runnable Julian Rocks sites through the cooler, swellier months. The trench walls themselves are a highlight for photographers: narrow gaps and undercuts are stacked with nudibranchs, painted crayfish, mantis shrimp, moray eels and small reef fish, and Byron Bay Dive Centre markets this specifically as a macro site for exactly that reason.

At a larger scale, wobbegong sharks lie along the trench floor and under the overhangs, sea turtles pass through routinely, and leopard sharks are seen resting in the sandier sections during summer. In winter grey nurse sharks occasionally use the trench as well, sheltering from current the same way they do at the Cod Hole a little further along the same side of the island. Divers need reasonable buoyancy control to work through the narrower sections without brushing the walls, and surge can funnel unpleasantly through the trench in a decent swell, which is the main reason operators will skip the site on genuinely rough days rather than the more exposed Cod Hole logic of simply being too dangerous.

On a good day, though, Hugo's Trench offers the best combination at Julian Rocks of dramatic swim-through-style topography, rich macro life and a moderate, Open Water-friendly depth range, and it is often run as the second dive of a Julian Rocks double after the Nursery or Needles.

Both Byron Bay dive operators launch small rigid-hull inflatables directly off the beach: Sundive Byron Bay launches from The Pass at the northern end of Main Beach, and Byron Bay Dive Centre launches from the beach near the Wategos/Clarkes Beach end; check in first at the shopfront in town (Sundive: Shop 8, 9-11 Byron St; Byron Bay Dive Centre: Byron Plaza, 5/90-96 Jonson St), then walk down to the beach for the boat launch briefing. It is a short, often bumpy, beach-launch surf crossing before a 5-10 minute run out to Julian Rocks, so loose gear should be secured. No private-boat ramp serves the rocks directly; private boats normally launch from the Brunswick Heads river mouth or Ballina and run up or down the coast.

Julian Rocks sits fully exposed 2.5 km off Byron Bay, so conditions depend on the swell and wind direction rather than any tide window. Trips are cancelled or moved between the Nursery (sheltered west side) and the more exposed east/south sides depending on swell direction and size; a big easterly or south-easterly swell above about 2 m closes the outer sites but the Nursery can often still run. Visibility is genuinely tide- and current-driven here as warm East Australian Current water and cooler southern water meet around the rocks — it can change from 5 m to 20 m within a single day and even between two dives an hour apart.

Summer (Dec-Mar) is warmest (21-26°C) with the leopard shark aggregation and manta ray sightings; winter (Jun-Aug) is cooler (18-21°C) but usually clearer, with grey nurse sharks and migrating humpback whales visible from the boat. Heavy rain from the Brunswick and Belongil systems can dirty the inshore approach for a day or two but rarely affects the rocks themselves once you are out.

Enter one of the two parallel trenches near the top at 8-10 m, work down through the narrow gap looking for nudibranchs, crayfish and wobbegongs on the walls, exit at the deeper end around 17-18 m, and circle back over the top of the rock to the mooring.

Sundive Byron Bay (The Pass) – daily double and triple boat dives; Byron Bay Dive Centre (Wategos/Jonson St) – daily double boat dives, Mon & Thu-Sun.