Dee Why Wide is the premier deep reef on the northern side of Sydney, a broad rock platform sitting on the sand plain off Curl Curl that gives Advanced divers wall, gully and sponge-garden diving in clear offshore water. The reef rises from 32 m to a top at about 23 m. Its edge is a series of low walls and large tumbled boulders, with big gullies running from the reef top south to the sand at around 30 m, and the plateau itself is cut by cracks running north–south and east–west, some wide enough to swim along with walls either side, others just slots.

Under the boulders on the edge are small overhangs where eastern blue devilfish hover and ladder-finned pomfrets pack in. The fixed life is what most divers remember: small gorgonian fans, thickets of sea tulips, sponges in yellows and oranges, soft corals and hard bryozoan crusts on every vertical face, brighter than anything inshore because the water is clean. Kingfish schools cruise the edge, leatherjackets, yellowtail and sea pike drift across the top, giant cuttlefish court in the cracks in late winter, and wobbegongs and Port Jackson sharks lie in the gullies.

A large ship's anchor with its stock broken off lies on its side in one of the east–west cracks, evidently abandoned after an unsuccessful attempt to lift it. Pro Dive rates the site 'black' and Sydney Dive Charters runs it as an Advanced dive to about 30 m, keeping the deeper 30–36 m outer edge for a separate 'Deep' version. Bottom time is limited by depth rather than interest, and nitrox makes a real difference.

Visibility can be 30 m; more often it is 10–15 m with a surface current that needs managing. Dee Why Wide suits Advanced divers comfortable with anchored descents in open water and is the standard Deep specialty site for Manly operators. It is a reef dive of real quality rather than a wreck, and pairs with Bluefish Point or North Head for a shallower second dive.

Boat only, 2.4 km off the northern headland of Curl Curl Beach. Sydney Dive Charters (Little Manly ramp/Rose Bay, 07:00 Thursdays and Sundays), Dive Centre Manly and Pro Dive Manly reach it in 20–30 minutes from Manly; private boats from Roseville Bridge take about 35 minutes. Visual marks are the two orange silo-like structures on the headland at the north end of Curl Curl.

The reef cannot be seen from the surface; anchor on the south-eastern corner where the bottom rises from 32 m to 23 m, or use a shot line. No mooring.

Open ocean 2.4 km offshore with no shelter. Swell from any direction over about 1.5 m makes the anchorage and ascent uncomfortable, and operators cancel above 2 m or with more than 15–20 knots of wind. Current is the main variable: the East Australian Current pushes south along this stretch and can run hard on the surface while the bottom is calm, so a current line and DSMB are standard.

Visibility is often 10–15 m and can reach 30 m in winter blue water; summer thermoclines at 15–20 m can drop the temperature below 17 °C on the bottom. Morning dives before the north-easter are the norm; avoid the days after heavy rain.

Descend the anchor to the reef edge at 23 m on the south-eastern corner and drop over the edge to explore the boulders and gullies at 28–30 m first. After 10 minutes come back up onto the plateau and follow the second or third crack from the eastern end north into the reef, then turn east along a wall and north again, passing the old broken-stock ship's anchor lying in an east–west crack. Return to the anchor on a reciprocal and do a long safety stop on the line; deploy a DSMB if adrift.

Nitrox 30–32% recommended for the Advanced profile.

Sydney Dive Charters – regular Advanced/Deep double boat dives; Pro Dive Manly – lists Dee Why Wide as a 'black' (advanced) site and runs it most months; Dive Centre Manly – periodic deep dives and Deep specialty courses. Nitrox recommended by all operators.