The Coolooli was for many years regarded as the best wreck in the Long Reef group, a big steel bucket dredge whose gantry, bucket ladder and funnel gave it an industrial silhouette unlike anything else off Sydney. Built in 1955 at the State Dockyard in Newcastle for the NSW Maritime Services Board, she was an unpowered dredge of about 50 m length and 10–11 m beam, towed from port to port to keep channels open. Laid up before 1975, she was sunk deliberately on 19 August 1980 as part of the artificial reef program that had already claimed the Dee Why and Meggol.

She lies on her starboard side, oriented roughly north–south, on sand at 48 m; most of the dive is spent between 42 and 46 m along the high port side and the deck. The defining feature is the long bucket arm running toward the cutter bar at the bow, still recognisable as a chain of huge steel buckets. Aft of it the superstructure and the funnel used to offer a straightforward penetration, entering the funnel and exiting through a rust hole, and memorial plaques for diver Paul Cavanagh, who died here in 1994, were fixed inside it.

A major collapse after 2009 changed the wreck considerably, and photographs from 2021 show it much flatter, so penetration options are now limited and the structure should be treated as unstable. A dumb barge lies 20 m to the south and further barges about 200 m away, which is useful for navigation and occasionally confusing on a sounder. Marine growth is the surprise: ropes and rails are furred with pink and blue jewel anemones and the shaded steel carries sponges and ascidians.

Fish life is thinner than on the Dee Why, though very large jewfish have been recorded. Visibility is typically 12–15 m and current is rare, making it one of the calmer deep dives on the coast. It suits decompression-trained divers who want a genuinely different wreck from the usual colliers and ferries, and it remains an important site in Sydney's technical diving history.

Boat only. Charters and private boats usually launch from the Roseville Bridge ramp on Middle Harbour or Rose Bay/Manly in Sydney Harbour and run north up the coast past North Head, Manly and Dee Why (roughly 45–60 minutes at cruising speed), or from the Akuna Bay/Pittwater ramps and run south past Barrenjoey (similar time). There is no all-weather ramp on the Northern Beaches ocean coast itself.

The wrecks lie on a flat sand plain and cannot be seen from the surface; you need accurate GPS and a sounder, and must drop the anchor or shot line directly onto structure because it will not hold in the sand. A drifting decompression station with spare gas is the normal arrangement.

The Long Reef wreck ground is 4–5 km offshore in open water with no lee. Any southerly or north-easterly swell above about 1.5 m makes anchoring on the wreck and the long decompression hang unpleasant or unsafe; charters generally want under 1 m swell and under 15 knots. Surface current from the East Australian Current can run north–south across the site even when the bottom is still, so a drifting deco station or a strong anchor line is essential.

Visibility is best from late autumn through winter (15–25 m) when the water is clear and cool; summer brings warmer water but more plankton and thermoclines. Avoid the days after heavy rain when the Narrabeen and Hawkesbury outflows dirty the inshore water. Mornings before the sea breeze are calmest.

Descend to the high side of the hull at about 40 m. Follow the bucket ladder toward the bow cutter bar, cross to the superstructure and funnel (the classic swim is in through the funnel and out through a hole in its side, now much altered by collapse), then run the length of the deck edge back to the shot. Keep the barge 20 m to the south as a reference.

Ascend the line for staged decompression.

Decompression dive. Typical plans use trimix (e.g. 21/35) or air/EANx with 50% and/or 100% O2 deco gases; 20–25 minutes bottom time gives 30–50 minutes of decompression. Twin cylinders or CCR with bailout, reel/line for any penetration, DSMB and surface support boat mandatory.

Silt inside compartments; several fatalities have occurred on this wreck group, so treat penetrations as overhead dives.

No scheduled recreational charters. Sydney Dive Charters (Rose Bay/Manly) runs technical charters to the Long Reef wreck area on demand for T1/Tec45+ certified divers; otherwise private boats and technical dive clubs launching from Roseville, Akuna Bay or Rose Bay ramps. Expect a handful of visits per year.