Toms Reef is the neighbour of the Portsea Back Beach Wall, 300 m to its south-east in the same field of scattered limestone reef that lies off the Portsea back beach in Bass Strait, just outside the Heads. Where the wall is a single defined edge, Toms Reef is broken ground from 12 to 24 m: a patchwork of ridges, ledges and bommies of soft calcarenite that the sea has eroded into swim-throughs, valleys and overhangs, capped with light kelp and undercut into sponge-lined caverns. The Scuba Doctor lists the same headline species for both sites – crayfish, blue devils, weedy seadragons, seals and abalone – and calls it a fantastic site for the avid fish photographer.

In practice divers find the reef more broken and more three-dimensional than the wall, with more places for lobsters and blue devils to hide and a slightly shallower average depth that stretches no-decompression time. Sweep, old wives, magpie perch, boarfish and bluethroat wrasse are constant; snapper, kingfish and barracouta pass through; and fur seals from the Heads colonies frequently join the dive. Because it sits outside the Heads it is subject to the same constraints as every back-beach boat dive – low swell, slack-water Rip crossings, charters that cancel more often than they run – and it is generally dived as the second dive of a back-beach day or when the wall is occupied.

It is an Advanced dive by depth and exposure but not a technically demanding one in good conditions: current is slight and navigation over broken reef is by depth and compass back to the anchor. Toms Reef suits Advanced divers, photographers and anyone who has done the Heads walls and wants a Bass Strait reef with more fish and less tide.

Reached only by boat from Portsea, Sorrento or Queenscliff, crossing The Rip at slack water; 15–25 minutes from Portsea Pier. Charters (Dive Victoria, Bayplay, Red Boats) include it in back-beach days when the swell is low; private boats need Heads experience. Anchor on the reef top in 12–15 m and descend the line; recover on SMBs if drifting.

Trips are timed to the Heads slack-water tables, so expect an early start and a cancellation if the Bass Strait swell rises above about 1.5 m.

Same exposure as the Back Beach Wall: needs Bass Strait swell under about 1.5 m and northerly or easterly winds, and boats must time The Rip. A running south-westerly swell produces surge over the 12 m reef top. Current is slight.

Visibility is generally 10–20 m and best in winter.

Descend the anchor to the reef top at 12–15 m, work out to the deeper ledges at 20–24 m along one edge of the reef, then return across the top exploring the swim-throughs and overhangs at 15–18 m. Ascend the line with a safety stop.

Dive Victoria and Bayplay (Portsea) on back-beach days; Red Boats private charters; Melbourne clubs. Less frequently visited than the Back Beach Wall.