The 25 Deepest Dive Sites in Northern Territory

Maximum depth is the number a database can sort by, but it is not what makes these sites hard. Three things are: the environment (open ocean over 80 m, a sinkhole shaft, a tidal channel), the logistics (a boat that can find and hold a mark, a permit, a cave rating) and the distance to a chamber. Almost everything above 60 m on this list is dived by a small circle of technical divers and clubs, on rebreathers or open-circuit trimix, in specific weather windows.

The recreational reader should look at the shallow ends. Piccaninnie Ponds, Kilsby and Ewens Ponds put Open Water divers over water that is 60 to 100 m deep without taking them past 20 m. The Kanowna and Federal have no shallow options, but the Port Phillip Heads walls that lead down to Trimix Corner start at 12 m.

Victoria dominates. Bass Strait is shallow but the shipping lane past the Heads, Cape Schanck and Cape Otway has claimed liners, colliers and warships in 70 to 115 m, and Melbourne has the most active technical wreck community in the country to find them. South Australia's Limestone Coast supplies the sinkholes: the Shaft, the Chasm and a dozen deep cave systems, all managed by the CDAA. Western Australia has the Rottnest graveyard and the Nullarbor caves; New South Wales has the Fairwind and a run of 60 m-plus wrecks off Sydney and South West Rocks.

Queensland barely features, which surprises people. The reef is shallow, the deep walls of the Coral Sea drop from 20 m to 1,000 m without a floor to record, and the state's deep wrecks (the Yongala at 30 m, the Brisbane at 28 m) are recreational. Deep in Queensland means offshore, not down.

Below 40 m is technical diving by every agency's definition: decompression procedures, redundant gas, helium below 50 to 60 m. The sinkholes add CDAA ratings (Deep Cavern, Cave, Advanced Cave), most of which take years. Many of the wrecks are protected historic shipwrecks or war graves with permit systems run by the state heritage office; the site pages say which. The technical diving section explains the courses, and the courses directory lists the centres that teach them.