Portsea Hole is a deep sand-bowl off Portsea, dropping to around 30 m inside Port Phillip Heads. The walls are covered in invertebrate growth — sponges, ascidians, hydroids — and the site is famous for big schools of bullseyes hanging in the bowl, plus blue devils, banjo sharks, big rays and the occasional grey nurse cruising through in summer. Bottom time is short at 30 m so it's strictly an advanced dive, and like every site inside the Heads it's slack-water only — Bass Strait water moves hard through here. Boat access from Sorrento or Queenscliff, with charter operators timing dives to roughly 30 minutes either side of slack. Best in light northerlies with swell under a metre. Use the live 7-day wind, swell and tide forecast on this page to plan your slack window.
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.