Lady Julia Percy Island sits about 8 km offshore from Port Fairy on Victoria's south-west coast — a volcanic-rock island in around 18 m of Bass Strait water with one of the best dives in western Victoria. Marine life is exceptional: huge kelp forests, sponge gardens, gorgonian fans, big crayfish, abalone, weedy seadragons, blue devils, schools of bullseyes and sweep, plus the resident Australian fur seal colony numbering hundreds of animals that will buzz divers playfully when conditions allow. Boat access only, from Port Fairy. Best in light north-east winds with swell under a metre and tide near slack. Use the live 7-day wind and swell forecast on this page to plan. Advanced divers — exposed open ocean, 8 km offshore, current around the island corners, fur seal interactions need respect (give them space, let them come to you), plan around a settled forecast.
How far you can see underwater — measured in metres. 10m+ is great, 5–10m is workable, under 3m is murk. Driven by wind, swell, and recent rain.
Long-period waves rolling in from the open ocean. Direction matters more than height — a S swell hits Portsea hard, but an E swell rolls past. Period over 12 s = real ocean punch.
Offshore (N or NE) flattens the surface and clears the water. Onshore (SE through SW) chops it up and stirs sand. Calm or light offshore is the magic combo.
This site faces the open ocean. The exposure caption above shows which directions slam in. Anything from the opposite side gets blocked — that's the safest window.
Slack water — the 30 minutes either side of high or low — is calmest and clearest. Mid-tide brings the most flow. Plan to be down at slack, up before the run picks up.
Bass Strait sits 14–16 °C autumn–winter, 17–19 °C summer. Below 16° a 7 mm hooded keeps you warm for 60 min+. Drysuit if you're going long.