Flinders Blowhole sits on the south-east corner of the Mornington Peninsula near the Flinders township, with reef diving out to around 12 m. The site is named for the natural blowhole in the rocks above and offers a more sheltered dive than the open-ocean back beaches further west — the Flinders coastline tucks in slightly. Marine life is plentiful: crayfish, abalone, weedy seadragons, blue devils, schools of sweep, and sponge-and-kelp gardens through the reef channels. Shore entry from the Blowhole walking track is doable but a fair carry. Best on light north-easterlies with swell under a metre and tide near slack. Use the live 7-day wind and swell forecast on this page to plan. Intermediate divers — easier than Cape Schanck but still exposed open coast with surf entry on bigger swell days.
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.