Forrest Caves on Phillip Island's south coast is named for the sea caves cut into the cliffs above the dive site, with reef running out to around 12 m below. It's an exposed Bass Strait site with kelp-and-sponge reef, scattered bommies, sandy gutters, and the usual south-coast crew of crayfish, abalone, weedy seadragons, blue devils and schools of sweep. The caves themselves are above water but make for a stunning entry landmark. Shore access from the Forrest Caves car park involves a stair walk and surf entry — only worth it on flat days. Best on light north-east winds, swell under a metre and tide near slack water so the reef is calm. Use the live 7-day wind and swell forecast on this page to plan. Intermediate divers — surf entry, exposed coast, watch the rip running along the eastern end of the beach when swell is up.
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.