The ex-HMAS Canberra is a 138 m former Royal Australian Navy frigate scuttled off Ocean Grove in 2009 as a recreational dive site. She sits upright in 30 m of Bass Strait water with the superstructure starting around 15 m — multiple penetration points, big swim-throughs, and after 15+ years of immersion she's smothered in sponges, ascidians, schooling baitfish, blue devils, big snapper and resident grey nurse on the deeper sections. It's the headline wreck dive in Victoria. Boat-only access, run by charter operators from Queenscliff and Portsea. Best on light north-east winds, swell under 1.5 m and tide near slack so current is manageable. Use the live 7-day wind and swell forecast on this page to plan. Advanced wreck-trained divers only — depth, current, and the wreck is huge enough to get disoriented if you're not familiar.
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.