The William Salthouse is the most important historic shipwreck in Port Phillip and one of the most significant in Australia, and it is the one Heads site that cannot be dived without a permit. She was a three-masted wooden barque of 251 tons, built at Liverpool in 1824 and 27 m long, which spent seventeen years in the British colonial trade before her owners, Green and Co., sent her on the first commercial voyage from Canada to the Australian colonies. She left Montreal on 17 June 1841 with £12,000 of cargo – barrels of salt beef and pork, flour, cider, wine, timber and building materials – and on 27 November 1841, entering Port Phillip in a strong south-westerly, struck a rock off Point Nepean. With eighteen inches of water in the hold within the hour she was run onto the Popes Eye sandbar and lost.

What makes her extraordinary is the state of the cargo. The lower hull and its contents were sealed in sand and survived; when divers found her in 1982 barrels were still stacked in the hold, and the site remains the only known example in Australia of an intact early-colonial merchant cargo in place. Looting followed the discovery, and in 1983 she became the first shipwreck in Victoria protected by a declared zone. Heritage Victoria and the Maritime Archaeology Association of Victoria stabilised the site in the 1990s with artificial seagrass mats and sandbags, which have rebuilt the mound and slowed the scour. Today, in the words of the Scuba Doctor listing, the wreck 'appears as a raised sand hill about 3 metres high'; the superstructure is gone but the lower hull and assorted cargo remain preserved in the sand, with frames, planking and the ends of barrels visible where the sand shifts.

Diving her is a privilege rather than a recreation: a permitted, supervised dive in 8–12 m on a fragile archaeological site where nothing may be touched and fins must stay off the bottom. Divers with an interest in maritime history should seek out a permitted heritage dive – they are run occasionally by Queenscliff operators and the MAAV – and everyone else should give the marked zone a wide berth. Penalties for entering without a permit are severe.

Boat access only, 15 minutes from Portsea Pier or Queenscliff Harbour, but the wreck lies inside a 250 m protected zone declared under the Heritage Act in which entry, diving and anchoring are prohibited without a permit issued by Heritage Victoria (apply well in advance; permits are normally granted for supervised heritage or club dives). Permitted boats moor on the mooring provided or hold off the zone, and divers descend directly onto the sand mound. Scuba Doctor GPS is from 'Packo 2013'.

Dive flag mandatory – the West Channel is close by.

It is dived only on slack water, either at the end of the flood (SWF) or the end of the ebb (SWE); most operators prefer the flood slack so that any residual current sets into the bay rather than out to sea. Slack water at Port Phillip Heads does not coincide with high or low water: it falls roughly three hours after high or low water at Point Lonsdale, and the usable window is typically 20–40 minutes. Use the Ports Victoria / Port of Melbourne slack-water predictions for The Heads (also republished by charter operators and WillyWeather 'Rip Bank') rather than a standard tide table.

Inside the Heads it is sheltered from most swell, but a south-west swell over about 2 m still surges across the top of the wall and a westerly or south-westerly wind over 15–20 knots makes the boat work unpleasant; big seas outside drop visibility to a few metres for a day or two. Visibility is best in late summer and autumn (Feb–May) when the water is clear and the westerlies have eased; winter brings 11–13 °C water and bigger swells but often the clearest days after a run of settled weather. Heavy rain has little effect this close to the ocean.

The bank is shallow and open, so the tide runs hard across it – slack water only. Fine sand lifts easily; visibility is best on the flood slack after settled weather and a fin-kick on the site drops it to nothing.

Under permit and briefing only: descend onto the 3 m-high sand mound at 8–10 m, stay off the timbers and the artificial seagrass mats, and circle the mound at 11–12 m viewing exposed frames, the ends of barrels and cargo where the sand allows; no touching, no fanning, no anchoring. Ascend on the mooring or under a DSMB.

No regular operator. Access is by Heritage Victoria permit only; Dive Victoria Group and Red Boats have run permitted heritage dives on request, and the Maritime Archaeology Association of Victoria (MAAV) visits for monitoring. Do not enter the protected zone without a permit.