Williamstown Beach is the western suburbs' main swimming beach, a curve of sand on the southern side of the peninsula between the breakwater at its western end and a rock groyne at its eastern end, backed by the Esplanade, a life saving club and a much-photographed bandstand rotunda. The rotunda end is the eastern of the beach's two dive entries and the simpler one: gear up at the metered car park, walk down to the shelter, enter from the sand on the western side of the groyne and swim out. The bottom shelves gently through weed and sand to a scatter of small basalt reefs in 5-6 m several hundred metres out, and those reefs, plus the groyne rocks, are where the life is.

The site is known among Melbourne macro divers for its critters: short-head seahorses in the weed, southern blue-ringed octopus under rocks, decorator crabs, nudibranchs, cushion stars and urchins on the reef, southern bobtail (dumpling) squid on the sand, stingarees and southern fiddler rays half-buried, and shoals of southern cardinalfish and old wives in the reef gaps, particularly at night. Because it is close to the CBD, has easy access and shallow depth, it is a pleasant night dive and a good place for new divers to build navigation confidence. The two negatives are shared with the whole Williamstown shore: heavy small-boat traffic close inshore, which makes a flag and depth awareness important, and the loss of visibility after rain.

The western entry at the breakwater, 430 m away, is a little more sheltered and slightly richer, and the two can be linked by a long swim along the reef line.

From the West Gate Freeway take Melbourne Road into Williamstown and follow signs to Williamstown Beach on the Esplanade. Park in the metered car park at the rotunda between Garden Street and Giffard Street or on the Esplanade itself; on hot summer days parking is very difficult. The rotunda is on the beach in front of the car park, a carry of about 50 m across the sand.

Enter from the beach in front of the shelter on the western side of the groyne and swim straight out; small reefs lie offshore in 5-6 m. 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. Not diveable in strong southerlies.

Tide is flexible but high tide is best.

Enter west of the groyne, fin out on the surface to 2-3 m, descend and head seaward on a compass bearing to the small reefs at 5-6 m, work around them, turn at half gas and return on the reciprocal bearing to the rotunda, which is easy to see from the surface.

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.