Boyinaboat Reef is one of Perth's most popular dives, a compact limestone reef in about 6–7 m at the southern end of an inshore reef chain, just 75–100 m from the sea wall of Hillarys Boat Harbour. It lies within a Marmion Marine Park sanctuary zone, is closed to vessel traffic and is marked by four yellow buoys. An underwater trail of about ten educational plaques guides divers around the reef.

The reef is small enough to explore in one dive but full of structure. Passages cut through the limestone, opening and closing again, and there are ledges, small caves, undercuts and carvings. Sponges, tube worms, bryozoans, ascidians and corals grow on it, and the corals are a decent size for such shallow, cool water. Fish include bream, leatherjackets, wrasse, scalyfin, drummer, western blue devils, blue groper and schools of garfish on the reef top, with crayfish and Port Jackson sharks under the ledges. Seagrass beds surround the reef.

Howies' Boy in a Boat page places the site at Hillarys, so the two rows have been merged here.

The hardest part is getting there. The shortest route involves climbing down steep, slippery breakwater rocks at the T-junction; the alternative is a 400 m surface swim from the steps near the car park. Neither should be attempted in swell over about 1.5 m.

Boyinaboat suits Open Water divers with some shore experience, and it is an excellent snorkel for strong swimmers. Divers who prefer an easy entry can join a boat dive from Hillarys.

Take the Mitchell Freeway to the Hepburn Avenue exit and drive west about 5 minutes to two roundabouts; go straight at the first and left into Southside Drive at the second, then follow signs to AQWA and park free behind it. Option 1: walk 300 m along the concrete path to the T-junction, climb the brown boulder and descend 6–8 m of steep, slippery rocks, then swim under water for about 5 minutes. Option 2: use the small steps cut into the groyne near the car park and the concrete slope, then surface-swim about 400 m on a heading of 290° (10–15 minutes).

Image Dive & Charters also dives it by boat.

Perth's northern coast is far more exposed to ocean swell than the Cockburn Sound sites. Best with swell about 1 m or less, a period under about 11.5 seconds and light easterly winds. Swell over 1.5 m makes the breakwater entry and exit dangerous, and southerly or westerly winds complicate them.

Visibility is up to 10–15 m on good days, but the sand is easily stirred. Dive in the morning before the summer sea breeze.

Reach the reef (the yellow buoys) from the breakwater, descend in 5–7 m and circle the reef clockwise or anticlockwise through its passages, looking at the plaques of the underwater trail and under the ledges. Return to the breakwater on a reciprocal bearing, swimming under water to avoid boat traffic, and exit carefully.

Image Dive & Charters (Hillarys, weekend morning boat dives in Marmion Marine Park) and other Perth operators include it on boat and guided shore dives; widely dived independently.