Port Phillip — Portsea & Blairgowrie

Almost everything is scheduled around the tide rather than the clock. Slack runs roughly an hour later each day and the usable window is short, so charters out of Blairgowrie, Sorrento and Queenscliff leave at whatever hour it falls, dawn one day and mid-afternoon the next, and are back before the flow rebuilds. The piers carry no such constraint: park, walk out along the boards and get in when it suits. Most itineraries end up pairing one timed boat dive with unhurried shore dives either side of it.

Two very different environments sit within a few kilometres of each other. Inside the bay it is shallow, sheltered and sandy, with the piers acting as artificial reef: pylons crusted in sponge and ascidian, a scatter of debris underneath, and open sand where small animals sit fully exposed. Out through the entrance the ground falls away into sponge-covered walls and cut ledges washed by cold water drawn in from Bass Strait, and scuttled ships lie beyond it, deeper and colder than anything the piers offer.

The pier dives are what people travel for, and the reason is behaviour more than any species list: animals here sit in the open on bare sand and stay put while you work them, so one pylon and the patch around it can fill a dive. After dark the sand turns over and the octopus and squid come out. The winter spider crab aggregation is the other event. They gather in the shallows to moult, the timing slides by weeks from year to year and the piers they pick change, so locals track it week by week rather than booking months out. Rays move in to feed on the soft-shelled crabs.

This is cold-water diving and does not pretend otherwise: drysuits are common outside summer, the surface can be choppy, and the strongest months have the shortest days. What comes back in return is macro diving within an easy drive of a major city, most of it in a few metres of water and much of it reached without a boat. It suits photographers, night divers and anyone happy to dive the same pier repeatedly. Divers after warmth, coral or long sightlines should look elsewhere.