Skip to main content

Green Island Ecosystem

The ancient coral cay of Green Island is a very unique indeed. Out of the 300 sand cays on the Great Barrier Reef it is the only one with a rainforest. Formed around 6,000 years ago by a build-up of sand sediments, animal and coral deposits it’s become home to a diverse range of flora and fauna. It sits 27kms from Cairns on the north-western edge of the reef flat in what’s called an ‘inshore patch reef’.

Green Island Formation

Sand cays are islands that form on top of existing reef structures – they are basically large piles of sand, coral rubble, broken shells and other reef debris. Wave action pushes the rubble debris into a pile on the leeward, or calm side, of a reef flat. If conditions are just right, this pile of rubble grows into a small sand island.

Seabird droppings help cement the sand together so that it will not wash away with tides. They also provide nutrients for germinating seeds that wash onto the island. Over time, if conditions remain ‘just right’, the island can develop a complex ecology.


The exact age of Green Island is unknown however best estimates are that it is about 6,000 years old. Scientists know that all sand cays on the Great Barrier Reef formed since the last Ice Age, about 8,000 years ago, when low sea levels destroyed all previously existing sand cays.

A Protected Area

The Australian government recognises that Green Island is a very special place and has protected it in several ways:

  • The island is a National Park and all commercial activities are regulated by permits.
  • The reef and underwater habitats are part of the Great Barrier Reef Marine Park.
  • Both Green Island and its reefs are included in the Great Barrier Reef World Heritage Area, which gives it international protection under UNESCO.


Green Island’s climate is tropical, with a wet season (January to March) that brings an average yearly rainfall of over 2 meters. Mean air temperatures vary between 24°C – 31°C in summer (November – April) and 19°C – 23 °C in winter (June – August).

23.423.723.823.1 21.619.917.817.117.418.720.622.3
Avg rainfall
Avg rainy


Dec Jan Feb
ºC ºF
31.4 89 31.4 89 31.2 88
ºC ºF
23.4 74 23.7 75 23.8 75
Average hours of sunshine daily
Avg rainfall mm
178 395 450
Avg rainy days
10.7 15.6 16.4

Marine Life

The reefs surrounding Green Island Resort support a diverse range of habitats for a wide range of tropical marine life.

You can experience the unique underwater world surrounding Green Island Resort by snorkelling, diving or by glass bottom boat. Seagrass beds support a wide range of animals, from juvenile fish that use the grass for protection from predators to large sea turtles and dugong that feed on the seagrass. The reef around Green Island has over 190 different types of hard corals and over 100 types of soft corals.

Bird Life

Green Island attracts a wide range of land, sea and migratory birds that pass through the Great Barrier Reef on the way to nesting grounds. The island is one of the most significant bird colonies on the reef, and is called home by 35 different species of seabirds and 28 species of forest birds. Of the 134 different species of plants on the island, most were deposited there by birds after feeding in mainland forests.