Tonga
Best overall months to dive: Jul–Oct
Tonga is a Polynesian kingdom of about 170 islands in the South Pacific, roughly 2,000km northeast of New Zealand. Its draw for divers is one animal: humpback whales of the Oceania population, which breed and calve in Tongan waters during the southern winter. Swimming with them is legal only between 1 July and 30 October, only with licensed operators, and only on snorkel — scuba with whales is prohibited. Vava'u is the main whale-swim base; Ha'apai runs licensed swims too, and Tongatapu and 'Eua have a slightly longer sighting window.