Kelp Beds Reef takes its name from the Admiralty charts, which for a century marked this part of Lonsdale Bight for the forest of giant kelp that rose from 15 m to the surface and warned ships off the shoal. The Scuba Doctor listing records that the forest kelp has largely gone – 'due to uncertain causes (water temperature, urchins, boat traffic)' – but that the reef retains thicker kelp species covering its rock formations and bommies, and that it is notable for 'sponge gardens with appeal to photographers, fish spotters and crayfish hunters'. Depth is 8–23 m; the separate drift listing gives 10–21 m on the flood.

The ground is a field of low bommies and ledges standing on sand and rubble, each capped with Ecklonia and other kelps and undercut at the base, with the sponge gardens of the bight filling the flats between – orange, yellow and purple sponges, ascidians and bryozoans in a continuous carpet. The decline of the giant kelp is part of a wider Victorian story, and the site is one of the places where its loss is most visible; but the community that replaced it is rich, with crayfish under every bommie, nudibranchs and sea stars on the sponges, blue devils in the undercuts and the fish of the bight – boarfish, magpie perch, leatherjackets, old wives, wrasse – over the top. Zoo Reef, 31 m away, is named for its fish density.

The listing's warning that 'the currents can run fast and strong, providing fresh nutrients' is the operational note: the site is dived either at slack from a shot or as a group drift on the flood under a float, never on a running tide without one. It is a regular on the Queenscliff schedules as a second dive and a photographer's site, and it pairs with Boarfish Reef and 12lb Reef, which lie within 150 m.

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 12 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 10 minutes to the site.

The site is in the middle of Lonsdale Bight, 10 minutes from Queenscliff and 15 from Portsea; dived as a slack-water reef dive from a shot or as a flood-tide drift under a float. 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 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 the reef for slack water and the separate 'Kelp Beds Reef Drift' entry (10–21 m) for the flood; the listing warns 'the currents can run fast and strong' and recommends drift or slack diving only.

Slack option: shot onto a bommie at 10–12 m, work the kelp-covered rock and the sponge gardens between the bommies at 12–18 m and return to the shot. Drift option: descend the float line at the western end on the young flood and drift east over the reef toward Queenscliff, the boat following the float.

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.