How big is the Great Barrier Reef?

It stretches roughly 2,300 kilometres along the Queensland coast and includes around 2,900 reefs and some 900 islands. The marine park covers about 344,400 square kilometres.

What causes coral bleaching?

Mainly unusually warm water lasting for weeks. Heat-stressed corals expel the algae living in their tissues, turning white. If the heat is prolonged, many of them die.

Is the Great Barrier Reef dying?

The reef is not dead, and many areas have shown strong recovery in the past, but repeated mass bleaching since 2016 has caused serious damage. Scientists warn that its future depends greatly on limiting ocean warming.

A low island made of sand and coral rubble piled up on a reef by waves and currents. Heron Island is a vegetated coral cay with forest, nesting seabirds and turtles.

Can I explore the Great Barrier Reef in the app?

Yes. You can visit a coral cay modelled on islands such as Heron Island and explore its beaches, lagoon, reef flat and pisonia forest in interactive 3D.

The world's largest coral reef system, built by tiny animals along the coast of Queensland

Great Barrier Reef

3D landscape · Heron Island, Queensland, Australia

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The Great Barrier Reef stretches for roughly 2,300 kilometres along the coast of Queensland, from the Torres Strait in the north to near Bundaberg in the south. It is not a single reef but a vast network of around 2,900 separate reefs and some 900 islands, spread over an area larger than the United Kingdom. In this app you can visit a coral cay modelled on islands of the southern reef, such as Heron Island, and explore it in interactive 3D: white sand, shallow turquoise lagoons, the reef flat and a low forest full of seabirds.

Corals are animals, and the reef has been built over thousands of years from their limestone skeletons. The reef supports thousands of species of fish, molluscs, corals and other marine life, along with turtles, sharks, whales and dugongs. It is protected as the Great Barrier Reef Marine Park and was inscribed as a UNESCO World Heritage Site in 1981. Repeated mass bleaching caused by marine heatwaves has become the biggest threat to its future.

Key facts

Location: Queensland, AustraliaAlong the north-east coast, in the Coral Sea
Length: About 2,300 kmCommonly quoted figure from the marine park authority
Reefs: Around 2,900Individual reefs of many shapes and sizes
Islands: Around 900Including coral cays and continental islands; counts vary with definitions
Marine park area: About 344,400 km²Managed by the Great Barrier Reef Marine Park Authority
Model setting: A southern coral cayModelled on islands such as Heron Island
Reef builders: Hard coralsLiving with algae called zooxanthellae inside their tissues
Marine park: 1975Created by the Great Barrier Reef Marine Park Act
World Heritage: 1981Inscribed by UNESCO as a natural site

How corals build a reef

A coral reef is built by colonies of tiny animals called polyps, relatives of sea anemones and jellyfish. Each polyp has a soft body with a ring of stinging tentacles and sits in a cup of limestone, or calcium carbonate, which it builds beneath itself. As colonies grow and die, their skeletons pile up and are cemented together by coralline algae and other organisms, slowly building the structure of the reef.

Most reef-building corals depend on microscopic algae called zooxanthellae, which live inside their tissues. The algae photosynthesise and pass much of the sugar they make to the coral, giving it the energy to grow quickly; in return they get shelter and nutrients. The algae also give many corals their colour. This partnership needs clear, warm, sunlit water, which is why coral reefs grow in shallow tropical seas. Many corals on the Great Barrier Reef reproduce in a mass spawning, releasing clouds of eggs and sperm on a few nights after a full moon in late spring or early summer.

Coral cays and Heron Island

Coral cays are low islands made of sand and coral rubble that waves and currents have piled up on top of a reef. Over time, seabird droppings, seeds carried by birds and ocean currents, and the slow build-up of soil allow plants to take hold. Heron Island, at the southern end of the reef, is a classic vegetated cay, surrounded by a broad reef flat that is exposed at low tide.

The centre of Heron Island is covered in forest dominated by pisonia trees, which have soft wood and large, pale leaves. Pisonia seeds are sticky and cling to the feathers of birds, which spreads the trees between islands. Black noddies nest in the branches in huge numbers, and wedge-tailed shearwaters dig burrows in the sandy soil, filling the night with eerie wailing calls during the breeding season. From late spring to early autumn, green and loggerhead turtles crawl up the beaches to lay their eggs, and the hatchlings later race down to the sea.

Turtles, rays and reef sharks

The reef is home to thousands of species of fish, from tiny gobies to giant groupers. Clownfish live among the stinging tentacles of sea anemones, protected by a layer of mucus; parrotfish crunch on coral and algae and grind it up, producing fine white sand; and butterflyfish, angelfish and wrasses dart among the corals. Giant clams, sea cucumbers, starfish and colourful nudibranchs are also part of the reef community.

Six of the world's seven species of marine turtle are found in the marine park, including green, loggerhead and hawksbill turtles. Manta rays glide over the reef and visit cleaning stations, where small fish pick parasites from their skin. Reef sharks, such as whitetip and blacktip reef sharks, patrol the shallows, and dugongs graze on seagrass meadows near the coast. In winter, humpback whales migrate north into the reef's warm waters to give birth.

Bleaching, cyclones and starfish

When sea temperatures stay unusually high for weeks, corals become stressed and expel their zooxanthellae, leaving their white skeletons visible through clear tissue. This is coral bleaching. Bleached corals are not dead, and they can recover if temperatures fall soon enough, but prolonged or severe heat can kill them. The Great Barrier Reef has experienced mass bleaching events in 1998 and 2002, and then in 2016, 2017, 2020, 2022 and 2024, with more widespread heat stress and bleaching reported in 2025. Monitoring reports in 2025 described some of the largest annual falls in coral cover seen in decades of surveys in parts of the reef, although the picture varies between regions and the full effects are still being assessed.

Tropical cyclones are another natural force that can smash corals, especially on exposed reefs. Outbreaks of crown-of-thorns starfish, which eat coral, have repeatedly damaged large areas; the causes are thought to include nutrient-rich run-off from farmland, which may help starfish larvae survive. Reefs can recover from single disturbances over roughly a decade, but more frequent heatwaves leave less time for recovery between them.

The marine park and World Heritage

The Great Barrier Reef Marine Park was created in 1975 and is managed by the Great Barrier Reef Marine Park Authority together with the Queensland Government. The park is divided into zones: some areas allow fishing and other uses, while green zones, covering around a third of the park, are protected from fishing and collecting. Zoning, water-quality programmes, crown-of-thorns control and research into coral restoration are all part of the effort to protect the reef.

UNESCO inscribed the Great Barrier Reef as a World Heritage Site in 1981, recognising its scale, beauty and biological richness. In recent years UNESCO and its advisers have discussed whether to list it as World Heritage in Danger because of climate change and water quality; so far it has not been placed on that list, but its condition remains under close international scrutiny.

Surprising facts about Great Barrier Reef

Corals are animals, but most reef-building corals depend on algae living inside them for much of their food.
Bleached corals are not necessarily dead and can recover if the water cools in time.
Parrotfish grind up coral and algae and produce much of the fine white sand on coral islands.
Pisonia seeds are so sticky that they sometimes trap small seabirds.
Six of the world's seven species of marine turtle are found in the Great Barrier Reef Marine Park.
On a few nights each year, many corals spawn at the same time, filling the water with eggs and sperm.

Frequently asked questions

How big is the Great Barrier Reef?: It stretches roughly 2,300 kilometres along the Queensland coast and includes around 2,900 reefs and some 900 islands. The marine park covers about 344,400 square kilometres.
What causes coral bleaching?: Mainly unusually warm water lasting for weeks. Heat-stressed corals expel the algae living in their tissues, turning white. If the heat is prolonged, many of them die.
Is the Great Barrier Reef dying?: The reef is not dead, and many areas have shown strong recovery in the past, but repeated mass bleaching since 2016 has caused serious damage. Scientists warn that its future depends greatly on limiting ocean warming.
What is a coral cay?: A low island made of sand and coral rubble piled up on a reef by waves and currents. Heron Island is a vegetated coral cay with forest, nesting seabirds and turtles.
Can I explore the Great Barrier Reef in the app?: Yes. You can visit a coral cay modelled on islands such as Heron Island and explore its beaches, lagoon, reef flat and pisonia forest in interactive 3D.

Keep exploring

The landscapes in Ember’s Universe are procedural 3D scenes modelled on real places. The landforms, plants and light follow the real thing, but the details are generated, not mapped.

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