Portarlington Pier is the Bellarine's main northern pier, a long timber and concrete structure with a rock-wall harbour that shelters the local mussel-farming fleet and now the Melbourne ferry. It faces north across the widest part of Port Phillip, which puts the whole peninsula between it and the southerly weather; The Scuba Doctor notes simply that it is protected from southerly winds, and that is its greatest asset for divers. The dive itself is easy and sandy.

Depth under the pier is 2-5 m at high tide over a clean sand bottom with seagrass patches, and the pylons carry the mussels that Portarlington is famous for, along with sea squirts, sponges and algae. Among them live seahorses (Portarlington is one of the more reliable seahorse piers on the bay), pipefish, blennies, cardinalfish, small leatherjackets, sea stars and octopus, with fiddler rays and flathead on the sand and squid and dumpling squid at night. The outer rock wall adds ledges and boulders with more fish, and 40-70 m seaward of the wall sit small artificial reefs that are outside the pier's 30 m protection zone and attract snapper, leatherjackets and wrasse.

The site makes a nice night dive, sheltered and lit. Its limitations are traffic and shallowness: the ferry, the mussel boats and the public ramp keep the harbour busy and the water is barely 2 m at low tide. For Geelong and Melbourne divers it is a reliable, comfortable pier for training, macro and night dives on a day when everything with a southerly aspect is unworkable, and Steeles Rocks 1 km east and the Indented Head sites a few kilometres south-east make a full day of it.

Portarlington is 30 km east of Geelong via the Bellarine Highway and Portarlington Road, about 1 hour 45 minutes from Melbourne by road or 90 minutes by the Port Phillip Ferries service from Docklands, which berths at this pier. Park in the large foreshore car park at the pier (free, busy in summer and on ferry arrivals) and walk 50-100 m to the beach or the pier. Enter from the sand on the western side of the pier or by the steps on the pier, and keep clear of the ferry berth, the boat ramp and the harbour entrance.

The outer rock wall is worth following; the artificial reefs lie 40-70 m seaward of it. Exit on the beach.

Protected from southerly winds by the peninsula behind it, so it is the classic fallback when the Mornington Peninsula and Bass Strait sites are blown out by a southerly. Northerlies and north-westerlies push chop straight into this north-facing bay and make it uncomfortable. Dive at high tide for extra depth under the pier and the best clarity.

Visibility 3-6 m, better in winter, reduced after rain. No swell. Ferry, fishing-boat and ramp traffic is constant, so tow a flag and stay under the pier or along the wall.

Enter from the beach west of the pier, follow the pylons out to the head at about 5 m, cross to the rock wall and work along its outer base, optionally heading 40-70 m seaward on a bearing to the artificial reef modules, then return along the wall and under the pier to the beach. Turn at half gas.

No regular commercial operator – dived independently and by Geelong and Melbourne dive clubs; Bay City Scuba (East Geelong) and Dive Victoria Group (Queenscliff) are the nearest shops and use the Bellarine piers for training and night dives.