Mordialloc Pier is the standard south-eastern suburbs pier dive, a long timber jetty running out from the beach beside the mouth of Mordialloc Creek. It is a working recreational pier with anglers on it most days and a yacht club and boat channel beside it, and the dive reflects that: it is not pristine, and part of its charm is the junk. The bottom under the deck is sand and shell grit from 2 m at the landing to about 6 m at the head, dotted with a famous graveyard of shopping trolleys and a scattering of golf balls, all of which have been colonised by sponges, sea squirts and algae and now shelter blennies, gobies and small octopus.

The pylons carry mussels, tubeworms and sea squirts with Tasmanian blennies, southern cardinalfish, small leatherjackets and toadfish, and a careful look at the weed and debris turns up short-head seahorses, dumpling squid, southern calamari, puffers, sea stars, sand crabs and southern blue-ringed octopus, which are common here and should not be handled. Jellyfish drift through in late summer. Toward the beach the ground is richer, with a small reef and more crabs and rays on the sand.

It is a good night dive because the pier is lit and the landing gives an easy entry, and it is used by the Frankston and Cheltenham shops for training. The site's weakness is water quality: the creek beside it carries stormwater and visibility is poor for days after rain, and it is exposed to any wind with south or west in it. On a calm northerly evening at high tide it is a relaxed, easy hour with plenty of small life.

The Aspendale artificial reef and Tyre Reef lie offshore to the south-west for boat divers.

Mordialloc is 25 km south-east of the CBD via the Nepean Highway or Beach Road (about 35 minutes). The pier is at the southern end of Mordialloc beach beside the creek mouth; park in the foreshore car park off Beach Road (paid 8 am to 8 pm) and walk 100 m out onto the pier. Gear up at the car; there is a tap near the yacht moorings for rinsing.

Enter off the lower landing partway along the pier, swim out under the deck to the end and then all the way back to shore, exploring the small reef and sand near the beach. Exit at the landing or wade out on the beach.

Quite exposed: north or north-east winds are best, or very light winds from any other direction. Southerlies, south-westerlies and westerlies raise chop along the pier and stir the sand. Do not dive after rain, as Mordialloc Creek discharges beside the pier and visibility collapses.

Dive on the high tide for depth and clarity; visibility 3-6 m typically. No swell. Boats and jet skis use the creek channel next to the pier, so stay under the structure and tow a flag.

Good night dive with the pier lit.

Enter off the lower landing, follow the pylons out to the end (about 6 m), cross under and return along the other side, then continue past the landing into the shallows near the beach where the small reef and sand crabs are, and exit at the landing or beach. Turn at half gas at the pier head.

No regular commercial operator – dived independently and by Melbourne dive clubs and shop social programs (Aquability in Frankston and Scuba Culture in Cheltenham are the nearest shops and use the site for night dives and training).