The Sisters are two rock pinnacles surrounded by deep water off Cape Surville, and for many local divers they are the best dive on the Tasman and Forestier peninsulas. The walls drop vertically from the surface to a sponge-carpeted seabed, and Scuba Diving magazine has called the site one of the best wall dives in Australia. The character of the dive changes with depth.

The upper walls are covered in kelp and brown algae, but from about 25 m the rock is taken over by invertebrates, and from 30 m the seaward face of the Outer Sister 'blooms', as local photographer accounts put it, with colour becoming more intense at 35 m. Here the walls are covered in jewel anemones, soft corals, sponges in every colour and fields of sea whips up to 2 m tall, while huge schools of butterfly perch swirl off the wall. The Marine Life Network guide records vertical drop-offs, sea whips and bommies in 10-45 m, with zoanthids and sponges throughout.

The dive centre groups the Sisters with its deep sponge gardens, which require at least Advanced certification, with Deep Specialty for anything below 30 m. Divers regularly compare the intensity of colour to tropical reefs. Boarfish, banded morwong, real bastard trumpeter and rock lobster are common, and fur seals sometimes join divers on the ascent.

Because of the depth and exposure the Sisters are very weather-dependent and are only reached on calm westerly days, often only a few times a month. Bottom time at 30-35 m on air is short, so many experienced divers use nitrox for the shallower sections or plan the dive as a single deep excursion with a long ascent up the wall. For a photographer or an experienced diver visiting Eaglehawk Neck, this is the dive to wait for.

Boat access only. Eaglehawk Dive Centre's catamaran and Go Dive Tasmania's boat leave from the Pirates Bay jetty/boat ramp at Eaglehawk Neck (Old Jetty Road, off the Arthur Highway about 75 km and 1 hour 15 minutes from Hobart). The Forestier Peninsula sites lie north-east of Pirates Bay: the run across the bay and around Cape Surville takes roughly 15-25 minutes depending on sea state.

Private boats also launch at Pirates Bay; there are no public moorings on the offshore pinnacles, so boats drift-dive or anchor in sand well clear of sponge gardens and run a live-boat pick-up.

The Forestier Peninsula coast faces east and north-east into the Tasman Sea with no shelter from easterly weather. These sites need westerly or north-westerly winds and small swell (generally under about 1.5 m) from the east and south-east; north-easterly sea breezes that build through summer afternoons often shut them by midday, so trips run in the morning. Southerly groundswell wraps around Cape Surville and creates heavy surge on the shallow tops.

Currents are unpredictable and can run strongly around the points and pinnacles, especially on spring tides and when the East Australian Current pushes south in late summer. Autumn (March-May) gives the most frequent calm windows and the clearest water; operators decide on the morning of the dive.

Drop on the seaward (eastern) side of the Outer Sister, descend the wall to 30-35 m where the colour peaks, and work along the face with the rock on one shoulder. Ascend slowly up the wall through the sea-whip zone, make any deco or extended safety stop on the pinnacle's upper wall, and lift on an SMB for pick-up.

Over 30 m requires Deep Specialty with the operators. Nitrox 28-32% suits a 30 m profile; deeper sections to 45 m are within recreational limits on air but deco-conscious divers use twinsets or rebreathers for longer bottom times.

Eaglehawk Dive Centre – deep sponge-garden dives when weather allows (Advanced minimum; Deep Specialty for over 30 m); Go Dive Tasmania – 'The Sisters' (20-40 m+, Advanced/Deep) on its Eaglehawk boat days.