Cook Islands
Aitutaki is an almost-atoll in the southern Cook Islands whose large lagoon is enclosed by a roughly triangular barrier reef, served by local dive operators.
Aitutaki consists of a volcanic main island and a lagoon enclosed by a barrier reef shaped roughly like an equilateral triangle with sides of about 12 kilometres. The lagoon covers an estimated 50 to 74 square kilometres and contains numerous small coral and volcanic islets. It is widely described in tourism sources as one of the most scenic lagoons in the Pacific.