Gull Island, also known as Bird Rock, is the small rocky islet in the calm eastern bay under Cape Woolamai, and it is Phillip Island's easiest boat dive. Scuba Doctor describes a large rocky outcrop situated in a bay normally sheltered from adverse south-westerly weather, with small crevices and overhangs carrying colourful corals, sponges and zoanthids. The rock drops to a flat sand and weed bottom at 6–8 m, and the dive is a simple circumnavigation.

The interest is in the detail rather than the scale: the shaded overhangs at the base of the rock hold encrusting sponge in oranges and yellows, zoanthid mats and small colonies of soft coral, and every crevice seems to have something in it – conger eels are noted specifically, along with Port Jackson sharks in winter and spring, decorator crabs, hermit crabs and the occasional crayfish. Wrasse, leatherjackets and morwong are the resident fish, with schools of sweep off the corners and stingarees and fiddler rays on the sand. The weed beds around the rock are worth a slow look for seadragons, which occur along this coast although they are not recorded on the listing.

Because of its depth and shelter, Gull Island works as a training or check-out dive, a second dive after The Pinnacles, a snorkel for non-divers in the boat, and a fallback when the ocean side of the island is unworkable. Silver gulls and shearwaters nest on and around the rock and the cape's shearwater colony is protected by Phillip Island Nature Parks, so boats should not land. It is a modest site by Victorian standards but a pleasant, unhurried one, and its dependable shelter gives it a place on any Phillip Island boat-diving itinerary.

Launch at Newhaven boat ramp and run about 4 km south down Cleeland Bight – 10–15 minutes – staying inside the bight so the open bar is not crossed. Gull Island is the obvious rock off the beach under the cape's northern slopes. Anchor in sand in 6–8 m on the lee side.

The bight is shallow and weedy at low tide, so watch the sounder on the approach. Shore access across Woolamai Beach and the rookery is not permitted.

Scuba Doctor notes the bay is normally sheltered from adverse south-westerly weather, which is what makes Gull Island useful: when the Pinnacles and the cape's ocean side are blown out by the prevailing south-westerly, this corner of Cleeland Bight is often flat. It is open to the north-east and east, so a fresh easterly or a north-easterly chop makes it uncomfortable and stirs the sand. Tidal flow in the bight is mild but visibility improves on the incoming tide.

Best at high tide for clearance over the surrounding reef. Diveable year-round.

Descend beside the rock and circle it at 6–8 m, keeping the rock on the same shoulder; a full lap takes 30–40 minutes at an easy pace. Poke into the crevices and overhangs with a torch for conger eels and Port Jackson sharks, and check the weed flats on the sand edge for rays. Finish under the boat; no safety stop needed at this depth but a slow ascent is good practice.

No dive shop or dedicated dive charter is based on Phillip Island. Sites are dived by Melbourne clubs (VSAG, Melbourne University Underwater Club, Frankston/Peninsula clubs) and private boats launched at Newhaven or Rhyll; Mornington Peninsula shops (Dive Victoria Group, Portsea; The Scuba Doctor, Rye) run occasional Phillip Island days. Ocean Adventures Phillip Island (Cowes) runs seal-snorkel tours only.