Sandringham's breakwater is a piece of maritime recycling. When the yacht harbour was built and extended through the twentieth century, redundant hulls were sunk to form and reinforce the wall, among them the cable-laying steamer Francis Henty, whose remains lie in 3-5 m as part of the structure, and the J-class submarine HMAS J7, scuttled in 1930 and later incorporated into the harbour moorings just north of the breakwater. The dive is a shallow wander along a wall of boulders and old iron in 1-6 m, with more holes, plates and ledges than any natural reef on this stretch of coast, and consequently a lot of fish: leatherjackets, moonlighters, zebrafish, old wives, blennies, wrasse, cardinalfish in the shadows, sea stars, urchins and nudibranchs on the rock, and octopus, cuttlefish and dumpling squid at night.

Rays and flathead sit on the sand at the base and juvenile snapper school around the wall in summer. It is a regular night-dive venue because the harbour precinct is lit, the pier gives an easy entry and the water inside the wall is calm in almost any wind. The trade-off is boat traffic: the harbour is home to one of the biggest yacht clubs in the state and the fairway is busy, so divers stay on the breakwater and out of the channel.

For an easy, structure-rich dive with a bit of history in the southern bayside suburbs it is hard to beat, and the J7 is there for anyone wanting to extend the swim.

From Beach Road at Sandringham turn down Jetty Road to the yacht club and harbour car park (ticketed, busy on race days). The pier inside the harbour is the usual entry for divers: walk 100 m out along it and enter from the lower landing or ladder, or walk in from the small beach beside the breakwater root. The dive follows the outside of the breakwater rocks and the old hulks built into it, in 3-5 m, and can be extended toward the J7 submarine 150 m north, which is documented as a separate wreck site.

Exit at the pier ladder or beach. Stay clear of the harbour fairway and slipway.

The harbour side is sheltered in most winds; the outside of the breakwater is exposed to westerlies and south-westerlies and becomes choppy and silty in anything above a moderate onshore breeze. Best in easterly through northerly winds and on the top of the tide. Visibility 3-6 m on a good day, poor after rain.

No swell. Yacht traffic is heavy at weekends, so fly a flag and keep tight to the rocks.

Enter from the pier landing, descend to 3 m and follow the inside of the breakwater to its tip, round the end and work back along the outer face at 4-6 m where the old hulks and boulders give the most relief, turn at half gas, and return inside the harbour to the pier ladder. Do not cross the fairway.

No regular commercial operator – dived independently and by Melbourne dive clubs and shop social-dive programs (Scuba Culture, Aquability, Melbourne Diving Services run occasional shore-dive nights at bayside piers); Ricketts Point-based snorkel tours run separately.