Lonsdale Bommies is a cluster of limestone outcrops on the outer Lonsdale reef, in Bass Strait about a kilometre off Point Lonsdale light and a couple of hundred metres east of Lonsdale Arches. The Scuba Doctor listing gives a depth of 12–18 m, an Open Water rating, an ebb-only tide window, and describes the same nutrient-rich, current-fed environment as the Arches: 'the strong current flow in this area has created a nutrient-rich environment and subsequently prolific marine growth and the associated marine life'. It is also noted, tellingly, as 'a favourite spot for catching crays' – the site lies within the marine national park where taking lobster is now prohibited, but the population that made the reputation is still there.

The bommies are rounded outcrops rising 3–5 m from a sand and rubble floor at 16–18 m, separated by gutters, with undercut bases and encrusted flanks. They lack the arches of the neighbouring site but have more edge, more crevices and, for a photographer, more places to find southern blue devils, cuttlefish, nudibranchs and the ubiquitous crayfish feelers. Above the reef the fish are those of the whole outer reef – sweep, boarfish, magpie perch, wrasse and leatherjackets – and seals drop in from the Point Lonsdale haul-outs.

Operators use the Bommies as the second dive of an 'outside' day after the Arches, or as the first drop when the Arches is crowded. The conditions that apply are the same: ebb slack, no significant south-westerly swell, and a boat that can pick divers up from a DSMB if they finish downstream. The site is easy and the navigation forgiving, and it is a good introduction to Bass Strait reef for divers who have only dived inside the bay. The Scuba Doctor listing also records an alternative Geoff Rodda mark (-38.282283, 144.646533) that is inside the Heads and appears to be an unrelated site.

Boat access only. Charter boats leave from Portsea Pier (Dive Victoria Group, Bayplay) and Queenscliff Harbour (Dive Victoria Group, Red Boats); run time is about 20 minutes. Private boats launch at Sorrento Boat Ramp (Point Nepean Road, Sorrento, all-tide concrete ramp with trailer parking) or Queenscliff Boat Harbour ramp (Larkin Parade, Queenscliff), roughly 20 minutes to the site.

The site is on the outer Lonsdale reef just east of the Arches, reached through the entrance on the ebb. Skippers must call Lonsdale VTS (Point Lonsdale) or listen to VHF 12 for shipping movements before dropping divers, and must carry a dive flag; anchoring is not permitted in the shipping channel, so a live boat and a drop-shot or drift float is the normal method.

It is dived on the ebb slack or a gentle ebb only, when the outgoing tide leaves this side of the reef in relatively still water. 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.

Being outside or right at the entrance, it is exposed to Bass Strait swell: anything over about 1.5 m from the south-west or south, or a strong southerly/westerly wind against the ebb, produces standing waves in The Rip and charters cancel. Northerlies flatten the entrance and give the best days. 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. Open-coast exposure: dropped in any south-westerly swell above about 1.5 m.

Shot onto the reef at 12–14 m on the ebb slack. Work from bommie to bommie along the gutters at 15–18 m, checking the undercuts at the base of each outcrop for crayfish and the tops for cuttlefish and nudibranchs; navigate back toward the shot along the same gutters. Safety stop on a bommie top or under a DSMB.

Dive Victoria Group (Portsea and Queenscliff) – double boat dives to the Heads walls most days of the week, site chosen on the morning by slack-water time and swell; Bayplay Adventure Tours (Portsea) – weekend and holiday charters; Red Boats (Queenscliff) – weekend Heads charters; Melbourne clubs (VSAG, Power House Underwater Club, Scuba Diving Melbourne) run their own boats here regularly.