Great Astrolabe Reef

The Great Astrolabe Reef runs for around a hundred kilometres along the eastern and southern side of Kadavu, taking its name from the Astrolabe, Dumont d'Urville's ship, which struck it in 1827. It is a barrier reef with a lagoon inside, passages cutting through it, and outer walls dropping into deep water. Manta rays use cleaning stations on the inner reef seasonally, hard and soft coral cover the passes, and the diving is spread over enough sites to fill a week.

What you actually see

• The outer walls - drop-offs on the ocean side with hard coral and pelagics.
• The passages - cuts through the reef where current concentrates the fish.
• The manta cleaning stations - inner-reef sites where mantas come to be cleaned.
• The lagoon - sheltered water inside the barrier with patch reef and sand.

When to go

May to October is the drier season with the best visibility. Manta sightings are seasonal and operators know the pattern. Cyclone season runs November to April.

Honest expectations

Access is entirely through Kadavu resorts and their boats; there is no independent diving. Sea conditions frequently cancel outer-reef days. Coral bleaching has affected sections of the reef in recent warm years.

Nearby

Kadavu island is inside the reef, and Vunisea is the airstrip and administrative centre.