Green Island sits in the middle of the D'Entrecasteaux Channel off Middleton, halfway between the Tasmanian mainland and Bruny Island. The Marine Life Network guide describes a mud and shell-grit bottom in 5-10 m with rocky outcrops, thin seaweed growth and an interesting variety of birdlife, and calls the island very beautiful. It notes poor water exchange, which can reduce visibility.

Underwater the outcrops host thin seaweeds, sponges and sea squirts, with wrasse, leatherjackets and small reef fish, while the shell-grit flats between them are home to sea stars, hermit crabs, flathead and, occasionally, rays. The site is quiet and gentle, a pleasant shallow dive for divers with a small boat exploring the middle channel. It is not a spectacular reef, but it offers a relaxed dive in a lovely setting, and the birdlife – shorebirds and seabirds using the island – adds to the outing.

Do not land on the island or disturb nesting birds. Combine it with a dive at Zuidpool Rock to the south for a more varied day in the channel. The middle channel is heavily used by salmon farms, mussel leases and recreational boats, so check charts for aquaculture lease boundaries and keep clear of pens and moorings.

Visibility is best on a calm, dry day with an incoming tide from the south. A sounder helps locate the outcrops, which are small and scattered. Green Island is a good destination for a family snorkel from a small boat, and for new divers wanting a sheltered, shallow first boat dive.

Boat access. Middleton is on the Channel Highway about 50 km (1 hour) south of Hobart. Launch at Middleton or another channel ramp (Gordon, Woodbridge) and run out to Green Island, a few minutes offshore.

Anchor in the mud clear of the rocks; the island is a bird habitat, so do not land. Middleton has a small ramp and jetty; bring fuel and supplies from Kettering or Cygnet.

The D'Entrecasteaux Channel is sheltered from ocean swell by Bruny Island, but strong northerly and southerly winds funnel along it and raise a steep chop. Southerly swell entering from the Southern Ocean affects the southern channel sites. Visibility is moderate and often green-tinged from Huon River and local runoff, dropping after heavy rain; the Marine Life Network notes a possible slow tidal current at some sites.

Calm mornings in late summer and autumn are best; the channel can be dived year-round. The Marine Life Network notes poor water exchange here can reduce visibility.

Descend near a rocky outcrop, explore it at 5-8 m, then fin over the shell grit to the next outcrop, returning to the anchor on a compass bearing.

Underwater Adventures Tasmania – Channel and Bruny boat trips from Hobart; otherwise private boats from channel ramps (Kettering, Woodbridge, Middleton, Gordon, Alonnah).