Beach 10B takes its name from the numbered life-saving beach marker on the Lonsdale Bay foreshore between Queenscliff and Point Lonsdale, and it is one of a trio of tidal shore dives (with Cottage by the Sea Reef and Shortland Bluff) that give experienced divers a taste of Port Phillip Heads from the sand. From the beach the bottom runs out through seagrass beds in the shallows onto undulating rocky ground with sparse cover at 5-6 m, then across ridges of sand that rise to within 4 m of the surface at around the 10 m mark, and finally onto the good ground: ledges, deep overhangs, gutters and swim-throughs at 8-9 m that locals call Friendly Bommie. This outer reef is where the oceanic flushing shows.

The overhangs are lined with sponges, ascidians, bryozoans and jewel anemones, the gutters hold old wives, magpie perch, boarfish and leatherjackets, blue-throat wrasse and moonlighters work the tops, weedy seadragons appear along the seagrass edge, smooth stingrays lie in the sand channels and fur seals from Chinamans Hat sometimes come to look. It is a genuinely good dive, better than most boat dives inside the bay, and it is free. The price is tidal discipline: The Scuba Doctor describes the site as very current prone and best dived right on a slack water flood, and the streams along this shore are strong enough to carry an inattentive diver toward the Rip.

Dive it with someone who knows the local slack, keep a float up for the boats and jet skis that use Lonsdale Bay, and turn inshore the moment the flood is felt. Cottage by the Sea Reef is 290 m west and Shortland Bluff 540 m east.

From Queenscliff township follow The Esplanade west along the Lonsdale Bay foreshore toward Point Lonsdale; park in the small beachside car park at the intersection of The Esplanade and Stevens Street (free). Take the steps down onto the beach, a carry of about 50 m, and enter from the sand. Swim out over the seagrass to the reef, which deepens to 8-10 m a few hundred metres offshore.

Exit at the same beach, or, if the flood has started, at the beach further east. Time the dive for Port Phillip Heads slack water before the flood.

Protected from northerly and westerly winds; faces south-south-west, so southerly winds and ocean swell entering the Heads make it rough and surgy. Best with offshore northerlies after a few calm days. Very current-prone: dive right on slack water at the turn to the flood, using Port Phillip Heads tide tables and allowing for local delay, and be out or inshore before the flood builds.

Visibility 5-12 m on a clean flood. Heavy boat and PWC traffic; a float and flag are essential.

Enter at slack water before the flood, swim out over the seagrass and undulating rock at 5-6 m, cross the sand dunes to the ledges and swim-throughs of Friendly Bommie at 8-9 m, explore the overhangs and gutters, and turn back inshore after 20 minutes or as soon as current is felt, letting any early flood push you east. Ascend in the shallows with the float up.

No regular commercial operator – dived independently by experienced local divers and Queenscliff clubs; Dive Victoria Group (Queenscliff) can advise on slack water.