St Helens Island is the premier boat dive of the St Helens area, rated 8 out of 10 by the Marine Life Network guide. It is a granite island off St Helens Point with dramatic underwater topography, where the granite drops away abruptly into 15-20 m. The guide describes long-snouted boarfish, trumpeter, colourful sponges and strapweed, and good visibility thanks to the island's position in clean ocean water.

Getting there requires crossing the Georges Bay bar, which limits trips to good conditions, and the island is exposed enough that the skipper must pick the lee side on the day. The reward is a clean-water granite wall with the kind of sponge growth normally associated with Bicheno.

St Helens Island suits Advanced Open Water divers with a capable boat. It has been largely neglected since the regional guide was written, and it would reward exploration by divers with a sounder.

The north-east coast from St Helens to the Bay of Fires is built of the same orange-lichen granite as Freycinet, and under water it forms rounded boulders, cracks and swim-throughs. The regional guide notes damage from the long-spined black sea urchin (Centrostephanus rodgersii) on several sites; this urchin has spread south with the warming East Australian Current and grazes kelp and weed down to bare 'barrens', so expect patches of bare rock among the weed.

The north-east sees far fewer divers than Bicheno or the Tasman Peninsula. There is no regular charter boat, so most diving is done by Launceston club members and visitors towing their own boats, and conditions are checked on the morning rather than booked in advance. The nearest hyperbaric chamber is the Royal Hobart Hospital, more than three hours' drive away; Launceston General Hospital has no chamber, so evacuation planning and oxygen on board matter here.

St Helens is on the Tasman Highway (A3), about 2 hr (165 km) east of Launceston and 3 hr 15 min from Hobart. Boats launch inside Georges Bay (St Helens town ramps or the St Helens Point ramp) or at Binalong Bay. The Georges Bay bar can be dangerous in easterly swell and on an ebbing tide; check MAST advice and cross only in good conditions.

From the St Helens Point ramp cross the bar and run south-east to St Helens Island, roughly 15-20 minutes. The island is steep-sided with no landing; divers are live-dropped on the lee side.

The St Helens and Bay of Fires coast faces east and north-east into the Tasman Sea, so easterly and north-easterly swell over about 1.5 m, and the common summer NE sea breeze, make it rough; the Georges Bay bar breaks in easterly swell. Westerly and south-westerly winds blow offshore and give the flattest seas and clearest water. Southerly swell wraps around St Helens Point.

Visibility falls after rain when Georges Bay drains tannin-stained water on the ebb. Choose the lee side of the island for the day's swell.

Drop on the lee side at 10 m, follow the granite as it falls away to 15-20 m, and work along the face looking at the sponges before returning shallower for a safety stop. Turn the dive at half gas (thirds where current or overhead sections are involved), deploy an SMB before surfacing for the live-boat pick-up, and complete a 3-minute safety stop at about 5 m where depth allows.

East Coast Scuba Centre (124 Binalong Bay Road, St Helens) is listed by Wikivoyage as offering dive and snorkel equipment hire - current trading status and whether it runs boat dives are unconfirmed. Otherwise sites are dived from private boats and by Launceston clubs and Tasmanian Divers (Launceston) on occasional trips.