Information on Green Island

Green Island is a very unique island. It is one of 300 sand (coral) cays on the Great Barrier Reef, but it is the only one with a rainforest.

Green Island In Brief


Green Island and its reef is very close to the mainland, lying only 27 km (16 miles) from Cairns. The island sits on the north-western edge of the reef flat. The surrounding reef is classified an ‘inshore patch reef’.

» Green Island Location Map

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 reef are included in the Great Barrier Reef World Heritage Area, which gives it international protection under UNESCO.

What is Sand Cay?

Green Island Fact and Figures
Island Area 15 ha / 37 acres
National Park Area 7.93 ha
Reef Area 1,200 ha
Length 660 m
Width 260 m
Circumference 1.6 km
Maximum Height 4 m

Sand or coral 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, but best estimates are 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.