The Herald Cays are two small, vegetated sand cays in the central Coral Sea, part of the former Coringa-Herald National Nature Reserve, now within the Coral Sea Marine Park and the Coringa-Herald and Lihou Reefs and Cays Ramsar Site. Marinelife.org.au describes the reserve, which also includes the Magdelaine Cays and Coringa Islets, as home to 745 species of molluscs and 400 species of fish, with green turtles nesting from November to April.

The cays are among the most isolated places in Australia. Parks Australia notes that the reserve holds the marine park's last remaining stands of Pisonia grandis forest, and North East Cay has been closed to the public to protect it. Seabirds nest in large numbers across the reserve.

Diving here is expedition diving in the truest sense. Specific dive sites are not named in the sources consulted.

The Herald Cays suit experienced, self-sufficient divers on well-equipped vessels. The main attractions are isolation, pristine habitat and wildlife, including turtles and seabirds, rather than any particular underwater feature. Visitors must follow Parks Australia's island access guideline, cleaning equipment and footwear, carrying no soil or seeds, and running vessel pest control, to protect the cays from introduced species.

There is no scheduled dive operator. Access is by private expedition charter, research voyage or cruising yacht with Coral Sea experience, self-sufficient for several days and carrying compressor, oxygen and satellite communications. From Townsville or Cairns the passage is roughly 350–450 km, typically 1.5–2 days each way; anchorage is in the lee of the reefs.

North East Cay in the Coringa-Herald group is now closed to the public to protect its Pisonia forest. Commercial tours need Parks Australia authorisation, and some islands are closed to landing.

These are remote oceanic reefs with no shelter from the south-east trades beyond their own reef rims, which blow 15–25 knots for much of April to October and make the multi-day open-ocean passage rough. Expeditions target calm windows, most often September to December; the lagoon anchorages give protection in moderate trades but the outer walls are dived only in light winds. December to April is cyclone season and trips are rarely scheduled then.

Currents on the walls and through passes can be strong; visibility is usually 30 m or more.

Dive the outer reef slopes and walls from a tender in calm weather, staying above 30 m; use the lagoon side for easier dives. Do not land on closed islands and keep well clear of nesting seabirds and turtles.

No regular operator – occasional private expedition charters, research voyages and cruising yachts only; any commercial tour requires Parks Australia authorisation.