A: It is safe to swim all year round in Cairns, Port Douglas and the Great Barrier Reef but it is highly recommended that you wear a lycra suit when entering the water in the warmer months of November-April.
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Take care when diving and snorkellingBe aware of where your fins are and avoid touching anything with them. Don't rest or stand on coral. If you must stand up, make sure it is on sand or use rest stations. Observe animals rather than handling them directly, and avoid blocking the path of free swimming animals.
Snorkelling. The sites in the Great Barrier Reef are shallow enough so that you can easily explore everything below the water's surface. The water in these parts is pleasantly warm and ideal for novices. There are plenty snorkelling expeditions from the main towns along the coasts.
The Great Barrier Reef is also prone to thunderstorms and the occasional cyclone. If you want reliably good underwater visibility, summer might not be the best time as rain and storms can cause the water to become murky. It's not all bad though.
Avoiding stinger seasonWhen you snorkel on the Great Barrier Reef during May to October you will avoid the peak stinger season. This is where box jellyfish and irukandji jellyfish are around. These jellyfish are around all year, they are more common during the warmer months.
Species of Sharks on the Great Barrier ReefFirst let us say this, there are no Great White Sharks on the Great Barrier Reef. The water is far too warm for them. With that sorted, these are the types of sharks you might see on the Great Barrier Reef.