Mona Vale's northern headland carries the Mona Vale Headland Reserve and the Bongin Bongin Bay lookout, and below it a rock platform gives access to one of the few documented shore reefs on the middle Northern Beaches. Vizzbud describes a reef that 'runs from shallow kelp beds near the surface down to sand at around 12–15 metres', rated Open Water with an 8 m average, entered best from the platform or by wading from the northern end of the beach at higher tides. The headland divides Mona Vale's open surf beach from the sheltered Basin (Bongin Bongin Bay) to the north, so the two sides give a rough-weather and a calm-weather option a few hundred metres apart.

The reef is boulder and ledge sandstone with kelp above and sponges beginning on the shaded faces at depth, ending at a sand line where weedy sea dragons live along the margin at about 12 m. Wobbegongs and blue groper are the reliable sightings, with red morwong, cuttlefish, Port Jackson sharks in winter and passing kingfish along the outer edge, which drops off quickly. Visibility is 5–12 m, best on winter westerlies.

The entry is the usual Northern Beaches platform problem: fine in a westerly with under a metre of swell, dangerous in a northerly, with surge on the rock and a longshore drift when the swell is running. Mona Vale is unusual in having a dive shop, Dive Spear and Sport, a few minutes away for fills and local knowledge. The site suits experienced Open Water divers and locals; combined with Bongin Bongin Bay on the northern side it gives a flexible half-day.

Details are from Vizzbud and should be confirmed on site.

From Pittwater Road, Mona Vale, take Surfview Road to the free car park at Mona Vale Headland Reserve on the northern headland (fills on summer weekends; street parking nearby). Walk 100–150 m down the path to the rock platform below the reserve. Enter from the platform, or at high tide wade out from the northern end of Mona Vale Beach to reach the reef.

Avoid it in northerly swell over 1 m. Exit at the platform or through the beach.

The beaches between Narrabeen and Palm Beach face east to north-east and are open to the full Tasman swell; anything over about 1 m from the north-east or east makes the rock-platform entries a wash zone and puts surge across the shallow reefs, and a southerly swell wraps around the headlands. Choose mornings with under 1 m swell and a westerly or light north-easterly, on the top half of the tide so the platform edges are covered. Visibility is 5–12 m on winter westerlies and drops after rain when the lagoons open.

There is no dive shop north of Brookvale except Dive Spear and Sport at Mona Vale, so fills and advice are limited; these are independent divers' sites. The Mona Vale headland is exposed to north and north-east swell, with surge on the platform and some longshore current in northerly conditions; the outer reef drops off quickly.

Enter off the platform, descend through the kelp at 3–5 m and follow the reef east and north-east down to the sandy margin at 12 m where sea dragons are found, look under the boulders for wobbegongs, then turn at half air and return shallower along the reef to the platform.

No scheduled operator; Dive Spear and Sport at Mona Vale is the local shop for fills, gear and advice and occasionally organises local dives. Otherwise independent divers.