The breakwater at the western end of Williamstown Beach is the best of the three Williamstown shore dives and one of the better critter dives within 15 km of the Melbourne CBD. A short rock wall runs out from beside the life saving club into water that deepens to about 5 m, with basalt reef, boulders, seagrass and sand beyond it, and because the wall is fished from and the reef is rarely disturbed the invertebrate life is remarkably dense. The list reads like a Port Phillip macro checklist: short-head seahorses in the weed at the base of the wall, southern blue-ringed octopus in the rock gaps, five-armed cushion stars and urchins on every surface, decorator crabs, nudibranchs in variety, southern bobtail squid buried in the sand at night, stingarees and southern fiddler rays on the flats, and old wives and clouds of southern cardinalfish in the shadows of the boulders, the cardinalfish especially abundant on night dives.

Larger fish are few, as everywhere on the inner bay, but the volume of small life makes up for it. Depth is modest and the navigation is trivial (wall on one side, out and back), which makes it a good site for newly certified divers and for photographers who want to spend an hour in one spot. It is 500 m east of the Jawbone Marine Sanctuary boundary and the Jawbone entries are the natural next step for anyone who likes this site.

The car park is large and has toilets open into the evening, which is rare among bayside sites, and the western end of the beach is quieter than the rotunda end.

Follow the Esplanade, Williamstown, to its western end at Victoria Street; the large car park is west of the Williamstown Swimming and Surf Life Saving Club at the southern end of Victoria Street (pay-and-display, machine takes cards). It is about 25 minutes from the CBD. Walk 50-100 m to the beach and enter either from the sand at the western end of the beach or by the steps near the breakwater.

The dive follows the breakwater rocks out and the reef and weed beyond. Exit at the same beach.

Best with light to moderate offshore northerly to easterly winds, or light onshore south-easterly to north-westerly winds; strong southerlies and south-westerlies put chop onto the Williamstown shore and stir the silt. Dive at high tide, which is also when the intertidal reef is accessible to snorkellers. Avoid the site for two or three days after heavy rain, when Yarra and stormwater runoff cut visibility to a metre.

Visibility 2-6 m in good conditions, best in winter. No swell; the water is flat when the wind is still. Little background swell reaches here.

Check the water before suiting up; if there is white water on the breakwater, do not dive.

Enter at the western end of the beach, follow the breakwater rocks out along their base at 2-4 m to the end, continue out over the weed and reef to 5 m, turn at half gas, and return along the other side of the breakwater or the same line to the beach.

No regular commercial operator – dived independently and by western-suburbs dive clubs and Melbourne shop social dives; no shop is based in Williamstown, so fills come from Dive Victoria Group or Scuba Culture.