The Ribbon Reefs, north of Cairns and reached by liveaboard, hold the best-known diving. The Cod Hole is famous for its enormous, curious potato cod, and in June and July these reefs host the world's only known predictable aggregation of dwarf minke whales — a small number of permitted operators run swim-with-whale encounters under strict rules.

The southern cays, particularly Lady Elliot and Heron Island, offer the best shore-based snorkelling on the reef. Manta rays cruise the cleaning stations, and green and loggerhead turtles nest on the beaches from about November to February, with hatchlings emerging from January.

The outer reef day trips from Cairns and Port Douglas are how most people see the reef: pontoon platforms with guided snorkelling and introductory dives. The coral here is heavily visited but the fish life is excellent and the logistics are effortless.

The Whitsundays in the centre combine fringing reef with island walking, and are the practical choice for a sailing-based trip rather than a dedicated dive one.

The dry season from June to October brings the best visibility and calmest conditions, and coincides with minke season and with humpback whales migrating along the coast. Coral spawning happens over a few nights after the November full moon.

Practicalities

A reef environmental management charge applies to most tours and is usually included in the fare. Stinger season runs roughly November to May, when full-body suits are standard on the water.

Be realistic about condition: repeated mass bleaching events have hit parts of the reef hard, and quality varies enormously between sites. Operators who visit multiple reefs and can move with conditions give a better picture than a fixed pontoon — and choosing a High Standard Tourism-certified operator directs your money towards those doing monitoring and restoration work.