The Bay of Islands is the place the Bay of Islands Coastal Park is named for: an irregular, semi-circular bay 5 km west of Peterborough with a dozen or more large limestone stacks and islands scattered across it, together with reefs and rocks, below 10–20 m limestone bluffs. It has the drama of the Twelve Apostles with a fraction of the visitors, and unlike the Apostles it has a boat ramp. Underwater the stacks are limestone pillars rising from a sand and reef floor in 10–20 m, their bases undercut into ledges, overhangs and small caves and their walls covered in kelp on the lit faces and sponges, ascidians, bryozoans and hydroids in the shade. Sand channels run between them. Crayfish are abundant in the undercuts, abalone on the lower walls, and the fish life is rich for the coast: blue-throat and senator wrasse, magpie perch, sea sweep in schools, zebrafish, herring cale, boarfish under the ledges, Port Jackson sharks and rays on the sand, and Australian fur seals from the Lady Julia Percy and Cape Bridgewater colonies passing through. In settled autumn water with 10–15 m visibility, circling the base of one of the big stacks with the light coming through the kelp is as good as anything on the Victorian open coast.

The Scuba Doctor lists it at 2–20 m for Open Water and beyond and notes plenty of interesting structure to explore; the practical constraint is that the bay is less sheltered than Crofts Bay next door and the currents between the stacks pick up when the outer reefs are breaking. It is essentially a private-boat site, launched from the ramp at Boat Bay at high tide on a low swell, and it rewards a group with their own boat and a settled forecast far more than a casual visit. A dive flag is essential because the ramp is busy with cray boats in season. For most visitors the bay will be a lookout; for a few it is one of the best-kept secrets of the Shipwreck Coast.

From Peterborough drive 5 km west on the Great Ocean Road and turn left onto Boat Bay Road, which leads down to the Bay of Islands boat ramp, car park and picnic area at Boat Bay. The ramp gives direct access to the stacks and reefs of the bay, most of which are within 500 m to 1 km of the ramp – a five-minute run. The beach beside the ramp is narrow and reached by a ramp and steps, and on a flat day divers snorkel out from it, but the bay is best treated as a boat dive.

Warrnambool (45 km) is the nearest dive shop and air.

Best dived at high tide when the reefs are fully submerged. The bay is less sheltered than Crofts Bay; the outer reefs break heavily in any swell and, when they do, currents run between the stacks. Aim for a south-west swell under about 1 m with light northerly winds; southerly and westerly winds and bigger swell make launching at Boat Bay and manoeuvring between the stacks dangerous.

The beach itself is generally calm because of the reef filtration, which is deceptive – check the outer stacks for white water before launching. Visibility clears after a few days of northerlies in autumn. Boat traffic from the ramp requires a dive flag.

Anchor on sand in the lee of one of the larger stacks in 10–15 m, descend and circle its base, working the overhangs, small caves and ledges at the foot of the wall, then cross the sand to a neighbouring stack if visibility allows. Keep the anchor position fixed with a compass bearing, turn at half gas and return for a 3-minute stop on the line. Watch for current between the stacks on a falling tide.

No regular operator – private boats launched at Boat Bay, Warrnambool Diving and club trips on calm days.