The Warrnambool breakwater was built in the 1880s to make a harbour of Lady Bay – the Edinburgh Castle, wrecked nearby in 1888, was carrying the cement for it – and its northern face is the town's easiest and most-dived site. The concrete and rock wall runs seaward from the point beside the Lady Bay boat ramp, and along its base in 3–9 m the kelp growth on the structure shelters an unusual concentration of small life. The Scuba Doctor lists seahorses (big-belly seahorses are regular), several species of leatherjacket, sea stars, boxfish, sea sweep, wrasse, gobies and blennies along the wall, with stingrays, flathead, flounder, pipefish and goatfish on the sand further out. Beyond the end of the wall the natural reef begins, with swim-throughs, kelp forests, fish and crayfish, and the reefs of the Old Aquarium and the Merri Marine Sanctuary lie a few hundred metres further on for those who continue on a calm day.

It is a beginner's dive in the best sense: a wall to follow out and back, a sand beach entry and exit, depth that rarely exceeds 9 m and a car park a minute away with toilets and a cafe. It is also the town's night dive, when the seahorses and cuttlefish are easiest to find, and the fallback when the exposed sanctuary sites are unworkable. The hazards are prosaic – boat traffic from the ramp 40 m to the south, which demands a dive float and flag, and surge that runs along the wall when swell wraps around the end – and visibility swings with the sand movement. Warrnambool divers use it constantly for training, check-out dives and quiet evenings, and visiting divers should treat it as the first dive of any stay: an hour here shows what the water is doing before committing to Stingray Bay, Thunder Point or the La Bella outside.

From the centre of Warrnambool follow Pertobe Road and Viaduct Road south-west to the breakwater, about 2 km; there is a large car park at the breakwater entrance and another off Viaduct Road. Gear up at the car and walk 50 m to the small beach between the breakwater and the Lady Bay boat ramp, entering from the sand and following the wall seaward on its northern side. Exit the same way.

Keep clear of the boat ramp 40 m to the south, which is busy with cray boats and recreational craft. Warrnambool Diving on Fairy Street is 2 km away for air.

The breakwater protects the inside from Southern Ocean swell and southerly winds, so this is the dive that works when the sanctuary sites are blown out; nonetheless the Scuba Doctor says conditions must be calm to dive here, because swell wraps around the end of the wall and the surge inside can be strong. Best on a low swell with north to west winds; easterly seas come into Lady Bay and stir the sand. Visibility varies considerably with the surge, from 3 m to 10 m.

Any tide, though high water gives more depth along the inner wall. Diveable on most days when the swell is under 1.5 m.

Enter from the beach, descend in 3 m and follow the base of the breakwater seaward with the wall on your left, checking the kelp and crevices for seahorses, leatherjackets and boxfish, out to the end in 8–9 m where the reefs, swim-throughs and kelp begin. Turn at half gas (or earlier if surge builds at the end), return along the same wall and surface at the beach, staying well clear of the boat ramp. Good as a night dive.

Warrnambool Diving (Fairy Street) – air fills, PADI courses, divemaster-led local shore dives on request; Daktari Surf & Dive (Warrnambool) – snorkel gear and guided snorkels; Warrnambool dive club members dive the sanctuary regularly on calm days. The breakwater is the standard training and check-out dive for the town.