Portsea Cray Reef is a patch of kelp-covered limestone ledges just off the end of Portsea Pier, in 5–12 m on the front beach, and the Scuba Doctor listing gives it an Open Water rating and the standard slack-water restriction but no description. The name records its history as a crayfish spot within a swim of the pier, and the reef is one of a chain of small reefs – Portsea Pier East Reef and West Reef are listed separately by Scuba Doctor – that run along the Portsea shore between the pier and Portsea Hole 800 m to the north-west.

The habitat is the shallow Heads-influenced reef of the Portsea front beach: ledges and gutters with Ecklonia and other kelps on top, sponges and ascidians on the undercuts, and sand and seagrass between. In such reef the residents are southern rock lobster in the ledges, weedy seadragons along the seagrass edge, big blue-throated and senator wrasse, old wives, magpie perch, leatherjackets, zebrafish and scalyfin, with cuttlefish in winter, rays on the sand and the seahorses and pipefish of the Portsea Pier piles a short distance away. Because it is within the marine national park the crayfish, once the point of the site, are now protected.

It is a modest, sheltered dive whose value is convenience: three minutes from the pier by boat, a float-swim for the fit, slack-water only but inside the bay and diveable in most weather except a northerly. The Portsea operators use it for check-out and training dives and as a fallback, and it pairs with Portsea Pier itself for a two-dive day from the one car park. Data confidence is low because the published record is position and depth only; the description of the fauna is drawn from the neighbouring Portsea front-beach sites.

Boat access in the listing, but it lies only 178 m off the end of Portsea Pier (Point Nepean Road, Portsea – paid foreshore parking, toilets, cafes) and is often reached from the pier by experienced divers swimming out on a float; the charter boats loading at the pier are on it in three minutes. Private boats launch at Sorrento ramp, 4 km east. The Portsea–Queenscliff ferry and pier traffic pass close by, so a flag is essential and the pier itself must not be swum under when the ferry is berthing.

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.

Scuba Doctor lists it for slack water; being on the front beach it is sheltered from all but northerlies, and it is a common fallback when the Heads are out. Visibility 5–12 m.

From the boat or the pier, descend onto the reef at 5–8 m at slack and work the kelp-covered ledges and gutters to the deeper edge at 10–12 m, looking under the ledges for crayfish and into the kelp for seadragons; navigate back toward the pier lights or the anchor and ascend with a flag.

Dive Victoria Group and Bayplay (Portsea) – used as a shallow training and check-out dive from the pier boats; also reachable by strong swimmers from Portsea Pier as an extension of the pier dive; private boats from Sorrento.