The Wilson Spit reefs are nine small patches of restored shellfish reef laid on the mud of Corio Bay's outer harbour as part of the same Port Phillip shellfish restoration program that built Moolap Reef 3 km to the west. Each patch is a mound of limestone rubble and recycled shell seeded with hatchery-grown native flat oysters and blue mussels, sitting in 8-9 m of water south of the shipping channel off the Wilson Spit shoal. Individually they are small, a few tens of metres across; together they form a scattered archipelago of hard structure that a diver can hop between on a compass bearing.

The point of diving them is ecological rather than scenic. Native shellfish reefs were once the dominant habitat of the bay floor and were dredged to extinction by 1900; watching them come back, with oysters spatting onto the shell, mussels clumping on the rubble and the whole mound greening over with ascidians, sponges, hydroids and algae, is a rare thing to see underwater. Fish move in quickly: snapper, leatherjackets, wrasse, gobies and blennies use the rubble, cuttlefish lay eggs in it in spring, and flathead, rays and the introduced Northern Pacific seastar work the surrounding mud.

The reefs are unmarked, unlit and rarely dived except by monitoring teams and the occasional Geelong club boat; they are also fished, so a flag, care with line and a clear view of the shipping channel matter. They are a good flat, shallow second dive after Moolap Reef for a small boat out of Limeburners Point or Point Richards on a still winter morning, and a reminder that some of the most important work in the bay is happening on featureless mud.

Launch at Limeburners Point (Geelong), Point Richards (Portarlington) or the northern-shore ramps at Avalon Beach and Geelong Grammar lagoon and run 15-30 minutes to the position. The nine reef patches lie within a few hundred metres of each other between about 38 07.13 S and 38 07.20 S, 144 30.22 E and 144 30.40 E; reef 7 is the usual mark. They are unmarked on the surface, so use a sounder, anchor on mud beside a patch and descend the line.

Not reachable from shore. Note The Scuba Doctor's page mislabels the region as Western Port; the site is in Corio Bay.

Exposed open-harbour water with no lee: light winds only. Best on the high tide in winter after dry weather; the Barwon and Hovells Creek plumes and wind chop reduce visibility, which is typically 2-5 m over the mud. No swell.

The Corio Bay shipping channel runs just north of the reefs and the Wilson Spit itself is a shoal; anchor well clear of both.

Descend the anchor line to 8-9 m at one reef patch, circle it looking for oysters, mussels and the fish sheltering in the rubble, then follow a compass bearing to the next patch a few tens of metres away and back, returning to the line at half gas and ascending with a stop at 5 m.

No regular operator – private boats, Bay City Scuba club boat and shellfish-restoration monitoring divers.