Fringing reef and approximately 1,100 of the Great Barrier Reef’s 1,625 species of fish surround Orpheus Island, a 3,212 acre, hilly national park island 42 nautical miles north of Townsville. Its most famous underwater feature is the garden of giant clams on its western side, in sheltered Hazard Bay, near the exclusive Orpheus Island Resort. Here, over a hundred massive bivalve molluscs laze on a sandy seabed, many grouped close enough together for their shells to touch. Aim your dive torch towards their golden brown, yellow and green mantles, which, thanks to a trick of the light, often appear iridescent turquoise or purple. Venture too close, though, and shells will partially close.

Mission Beach, 40km from the reef, is habitat of the magnificent cassowary, the world’s second heaviest bird. Look for smaller males minding chicks, lone females, and follow back their seed and fruit-filled scat between dawn and dusk on rainforest tracks – 1.5km Lacey Creek, 1.3km Fan Palm and 3.9km Bicton Hill. But keep your eyes open, particularly following rain, when these shy but fierce creatures will be scouting for fallen seeds and fruit.

Imagine floating in a lagoon just above a carpet of coral and sea cucumbers. A juvenile green sea turtle dances leisurely alongside you, regarding you with his big black eyes. In the protected waters surrounding Lady Elliot Island, a 45 hectare coral cay in the southernmost 344,400km2 Great Barrier Reef Marine Park, such turtle encounters aren’t unusual. Snorkel on the island’s eastern side, in front of Lady Elliot Island Eco Resort, and you’ll also see reef sharks, flowery rockcod and elegant manta rays. The island seduces nature lovers on land, too. From September to March, thousands of breeders – black noddies, crested terns, and others – come to nest and rear their young. Between November and March, endangered green and loggerhead turtles labour up the beach to lay eggs beneath the stars, and, from February to April, precious hatchlings race down the same beach.

Just off the Ribbon Reefs’ northerly tip, 12 nautical miles east of Lizard Island, is the Cod Hole. It is on many peoples diving bucket list thanks to its massive resident potato cod, which can push up to two metres in length and 100kg in weight. If your dive master is carrying fishy snacks, these grey-brown, blotch-covered, thick-lipped fish will approach as soon as you enter the water and follow your group around the underwater canyons like loyal puppies. The shallow (under 15 metres) feeding area depth and subject proximity make this an excellent site for underwater photography enthusiasts. However, your vessel must have a marine park-issued fish-feeding permit and feeding limits apply. Also, to avoid wiping away their skin’s protective mucous coating, refrain from touching them.

Coral gardens, clownfish, hawksbill turtles and relative proximity (60km) to Cairns make 4.2km2 Flynn Reef popular with live-aboard dive trips, day trip operators and tourist vessels. But it is worth sacrificing seclusion to meet its memorable resident, the endangered humphead (also known as a Napoleon or Maori) wrasse. This two metre long, multi-coloured fish lurks off the back of your boat sporting big lips, a hump on his forehead, a groovy facial pattern, and a permanently startled expression. This flirty fish is a hermaphrodite: when an alpha male dies, a female changes sex and becomes the new alpha. And curiously, this wrasse sometimes swims close enough to “kiss” your regulator. Perhaps he’s acquired a taste for bubbles?

The Ribbon Reefs – a series of slender outer reefs stretching northeast of Cairns near the continental shelf’s edge – are magnificent to behold, both underwater and from the air. Between June and mid-July, migrating dwarf minke whales, which grow up to eight metres long, appear off the southern end of Ribbon Reef #10 as well as around Ribbon Reef #3. Licensed operators Eye to Eye Marine Encounters offer bespoke minke whale research trips; when adult whales without calves are spotted less than 100 metres away (but no closer than 30 metres), snorkelers quietly enter the water and hang onto a mermaid line, floating and waiting for the inquisitive cetaceans to approach. If you’re still, the slender, pointy-snouted grey and white gentle giants will venture within a few metres. To avoid startling them, don’t make physical contact (it’s illegal) or use flash photography; if they’re comfortable, this profound experience could last for hours.

Last year UNESCO voted not to put Australia's Great Barrier Reef on world 'danger list' but the area is still considered to be under threat. Don’t miss our guide on to how to charter responsibly if you visit the area.