The Glennie Group lies off the western edge of Wilsons Promontory, a cluster of granite islands rising from around 25 m of Bass Strait water. The dive sites here are world-class on a flat day — kelp forests, sponge-and-gorgonian gardens, big crayfish, abalone, weedy seadragons, blue devils, schools of bullseyes and sweep, and frequent fur seal encounters from the Wilsons Prom colonies. Boat access only, charter out of Port Welshpool or Tidal River, with a long run across exposed water. Best in light northerlies, swell under a metre and tide near slack. Use the live 7-day wind and swell forecast on this page to spot a settled window. Advanced divers — exposed open coast, currents around the granite headlands, remote with limited bail-out, and the run out demands a settled forecast not just at the sites but along the route there and back.
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.