Point Gellibrand is the southern tip of the Williamstown peninsula, the site of the Timeball Tower, the old naval battery and the Coastal Heritage Park, and along its Port Phillip face the shore is a continuous run of basalt ledges and rock pools formed by the Newer Volcanics lava that flowed down to the bay from the west. The rock pools at Battery Road, also called the Bunbury Rockpools, are the entry. The first metres are shallow, uneven basalt full of pools and gullies, and the ground then deepens gradually into a broad reef of ledges, boulders and undercuts in 3-5 m before running out onto sand.

It is not a big or deep site, but it is unusually rich for somewhere ten minutes from the West Gate Bridge. The basalt is coated with encrusting sponges, tubeworms, mussels and algae, and the ledges shelter a surprising number of fish for an inner-bay reef: leatherjackets, wrasse, zebrafish, dusky morwong, blennies, cardinalfish and juvenile snapper, with rays and flathead on the sand. Its reputation among photographers rests on nudibranchs; large, colourful sea slugs are found in numbers on the undersides of the ledges and it is regarded as one of the most rewarding macro sites close to the city.

Octopus, decorator crabs, cushion stars and urchins round it out. The entry over slippery basalt at high tide is the only real difficulty, and shipping wash from the channel can surge across the platform, so the site is best on a calm day with a north-westerly. The wreck of the Albert William lies 450 m to the east for those interested.

With free parking, a playground and the heritage park behind it, it is a pleasant, low-key western-suburbs dive.

From Nelson Place, Williamstown, follow Battery Road south around the point past the Timeball Tower to Point Gellibrand Coastal Heritage Park. Free parking is available at either end of Battery Road; the playground car park is closest to the rock pools, a carry of about 50 m. Walk out over the basalt platform and enter at a gap in the rock pools at high tide; the rock is slippery and uneven.

The reef begins shallow and rocky and gradually deepens seaward. Exit back across the platform at the same spot, taking care with waves and footing.

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. The point is a little more exposed to easterlies than the beach sites to the west, so a north-westerly is ideal.

Shipping wash from the channel to the east can surge across the shallow platform.

Enter through the rock pools at high tide, fin out over the shallow basalt to 2-3 m, follow the ledges seaward and along the point at 3-5 m spending time on the nudibranch-rich undercuts, turn at half gas, and return on a reciprocal to the same gap in the platform.

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.