Offshore reefs around Cape Nelson on Victoria's Discovery Coast sit in around 25 m of water, around the volcanic headland just south of Portland. The cape is fully exposed to south through south-west swell and rarely sits flat, but the diving is excellent when it does — basalt reef structure, kelp gardens, sponge cover, gorgonian fans, big crayfish, abalone, weedy seadragons, blue devils, schools of bullseyes and sweep, plus pelagic visitors and fur seal interactions. Boat access only, from Portland harbour. 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 coast, currents around the cape corners, swell wraps in around the headland in tricky ways, plan around a properly settled forecast and have a back-up plan in case conditions change while you're on the water.
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.