Dobroyd Head is the bush-covered headland that forms the western side of North Harbour, facing Manly and North Head across a kilometre of water, and its foot is a long boulder reef inside the North Harbour Aquatic Reserve that the VIZ dive club has surveyed with a GPS float from Forty Baskets to Crater Cove. Diveplanit notes Reef Beach and Forty Baskets as the shore access. The northern section is unpromising: kelp in the first 4 m and then sand.

South of Reef Beach the terrain improves steadily – boulders with vegetation and sponges, then sponge gardens and walls that reach further offshore than the cliff line implies – and a small wreck lies on the sand at 12 m. Sandy bottom is at 10–12 m throughout. The club's species list from its scooter dives is long for the harbour: Port Jackson sharks (including a 25 cm juvenile), Australian angelsharks, crested horn sharks, a banded wobbegong, stonefish, moray eels, a juvenile hammer octopus, schools of kingfish, blue-and-yellow fusiliers, seahorses near Forty Baskets, sea urchins and sea tulips; sponges dominate the deeper southern boulders.

Four abandoned anchors jammed in crevices tell of the fishing boats that work the face. The problems are visibility and access. Visibility is 2–3 m at depth because of a layer of heavier-than-water particles on the harbour floor, which made the club's compass navigation unreliable; the southern half has no shore access, so it is a scooter or boat dive; and the Manly ferry passes at full power close enough to be alarming underwater.

Night dives reduce the boat risk. Dobroyd suits experienced, self-reliant divers and scooter enthusiasts who want the last unmapped stretch of the reserve, and it is best treated as exploration rather than a set-piece dive.

Park at the end of Beatty Street, Balgowlah Heights, and walk the Manly Scenic Walkway 700 m to Forty Baskets Beach and a further 700 m north along the coastal path to Reef Beach (a former nude beach, small and rocky). Enter from the sand and head south along the reef. The southern half toward Crater Cove has no shore access – the club's 3.2–3.8 km scooter itineraries start from Forty Baskets – and a small boat from Manly (10 minutes) can drop divers anywhere along the face.

Alternatively enter at Castle Rock Beach (Clontarf side) for the northern approach. Exit at the entry beach; there is no exit between Reef Beach and Crater Cove.

Deep inside the harbour these sites see no ocean swell; only a strong southerly or south-easterly wind raises a chop, and even then the dive usually goes ahead. What matters is water quality and tide. Dive on the incoming tide or at high water, when the flood brings cleaner ocean water up the harbour and the shallow margins have enough depth; low tide exposes rock and shortens the dive.

Visibility is normally 3–7 m and can reach 10 m on a winter flood; after heavy rain the harbour runs brown for several days and visibility drops to a metre. Boat traffic is heavy on summer weekends. Night dives are the best dives.

The Dobroyd face looks east across North Harbour to the Heads and is sheltered from ocean swell; the Manly ferry passes close and fast, and the heavy particle layer near the bottom cuts visibility to 2 m at depth even when the surface looks clear. Night dives are recommended by the club for the reduced boat traffic.

From Reef Beach descend through the kelp (first 4 m) to the sand at 10–12 m and follow the boulder edge south, where the terrain becomes progressively more complex with vegetation, sponges and then true sponge gardens and walls that extend further offshore than the surface suggests; locate the small wreck at 12 m if visibility allows. Turn at half air (or battery) and return north along the same edge; count the four abandoned anchors in the crevices as waypoints.

Scooter dives of 3.2–3.8 km return have been logged; plan battery turn-around conservatively.

No operator; VIZ dive club (mapping and scooter dives), independent divers, occasional boat drops by Manly charters as a sheltered alternative.