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What Is The Difference Between A Coral Reef And A Coral Cay?

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Gabby Boucher
Updated Thu 27 Jun 2024

The main difference between a coral cay and a coral reef is that a coral cay is a small, low island that rests on top of a coral reef. Both are abundant on the Great Barrier Reef, and Cairns is the perfect place for a trip to explore these wonders. There are lots of amazing Great Barrier Reef tours that depart Cairns daily for spectacular reef sites and coral cays at sea. Here is our complete guide to coral reefs and coral cays, as well as the best ones to visit near Cairns!

man snorkelling over coral reefs in the great barrier reef


What Is A Coral Reef?

A coral reef is an ecosystem in the ocean made of vast collections of corals. There are many different types of coral reefs and coral organisms. Most coral reefs are comprised of hundreds or thousands of coral polyps, which are the tiny living animals that we know as coral. Large groups of coral polyps bind together with calcium carbonate to create coral reefs of all shapes and sizes. These coral reefs create an important habitat for a vast array of marine life, and every organism plays a vital role in the underwater ecosystem. 

underwater coral reefs on the great barrier reef


Coral Reefs on the Great Barrier Reef near Cairns

Cairns is just a short flight or boat ride away from some stunning coral reefs on the Great Barrier Reef. There is a wide variety of reef sites to visit, all of which offer something different. You can see hard or soft corals, and corals of all different colours on the Great Barrier Reef. This is the largest coral reef system in the world, stretching over 2,300km along Australia's East Coast!

Outer reef sites near Cairns

The Outer Reef sites near Cairns grow up from the ocean floor. Barrier reefs tend to form in places of prior volcanic activity, and they can get massive! Outer reefs generally have lots of hard corals as well and are surrounded by deep water that is ideal for scuba diving. Popular Outer reef sites near Cairns include:

scuba diver posing underwater next to a coral reef


Fringing reef sites near Cairns

Fringing reefs grow along shorelines of landmasses. These coral reefs latch onto rocks, coastlines, and the edges of islands and grow upward and outward. Because fringing reefs are close to shore, they are easily accessible and great for snorkelling. Tours to fringing reefs usually allow for island exploration as well! 

The Whitsunday Islands, located about 500km south of Cairns, are one of the world's most famous locations for fringing reefs. Closer to Cairns, you can find fringing reefs growing around these islands:

aerial view of fitzroy island beach and fringing reefs


What Is A Coral Cay?

A coral cay is an island that forms on top of a coral reef. A cay, pronounced "key", is generally low-lying, small, and composed of sand or sediment. Ocean currents move the sediment around until it congregates in one location, forming a cay. So a cay is a special type of island. All coral cays can be considered islands, but not all islands are cays. 

couple walking on a sand island on the great barrier reef


Coral Cays on the Great Barrier Reef near Cairns

There are some gorgeous coral cays near Cairns that make fabulous day trips. Some cays are large and sturdy enough to support human life and infrastructure, such as Green Island. This is the most famous cay near Cairns, and it is technically a cay even though it is called Green Island.

Other cays are smaller, uninhabited, and more remote. For example, Vlasoff Cay is only accessible via helicopter from Cairns. Michaelmas Cay is a popular day trip from Cairns and is an important site for migratory birds on the reef, but it has no man-made amenities. 

Popular cays near Cairns

aerial view of green island and surrounding reefs


Should I visit a coral reef or a coral cay near Cairns?

Now that you understand the difference between a coral reef and a coral cay, let's compare tours. Coral reefs offer a variety of experiences for travellers. Heading to the Outer Reef is ideal for scuba divers because there is deeper water and more massive coral structures to explore. Snorkelling is also amazing on the Outer Reef. 

Coral cays offer a more tropical island experience. Here you can find soft white sand and clear turquoise water that is perfect for sunbathing, picnics, and romantic beach walks. You can often go snorkelling or scuba diving in the fringing reefs off the edge of a coral cay as well.  

For travellers who can't decide which reef experience is best for them, day trip combos and packages are a great way to see more. You can also find tours that combine a trip to the Outer Reef with a trip to a coral cay

See the best of the Great Barrier Reef from Cairns!

two travellers looking at michaelmas cay near cairns


For more advice on which Great Barrier Reef tours to choose for your trip to Cairns, contact our local travel experts!

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