Stingers are of particular concern in tropical Australian waters between November to May/June. In Cairns, we call this period 'stinger season'.

Predominantly a problem along the coast and not usually affecting the Great Barrier Reef, North Queensland's marine and estuarine environment is home to many interesting animals, including some harmful jellyfish collectively known as marine stingers. These small marine stingers are easy to avoid but can cause discomfort if you are stung, and some of the tropical species, such as the Irukandji and Chironex fleckeri (the Box Jellyfish) can be lethal. So, to ensure you enjoy your day at the beach or Great Barrier Reef, always remember to swim at a patrolled beach and look out for the safety signs. if visiting the Great Barrier Reef always use the lycra "stinger suits" offered. As well as protecting you from stingers they offer great sun protection. Sometimes there is a small fee charged as these suits are very lightweight and need to be replaced often.

Prevention

• Always swim at patrolled beaches, between the red and yellow flags.
• Look for and obey safety signs.
• Don't enter the water when beaches are closed.
• Ask a lifesaver or lifeguard for help and advice if you need it.
• Don't touch marine stingers washed up on the beach, they can still sting you.
• In tropical waters it is also recommended that you take these additional measures.
• Swim in the stinger nets where provided.
• It is recommended that a full-body lycra suit, or equivalent, be worn to provide a good measure of protection against marine stings, particularly during the stinger season, which generally runs from November to March.
• Enter the water slowly - this gives marine stingers time to move away.

From Wikipaedia - "Marine stingers are classified under the Phylum Cnidaria, being a group of animals that occur in polyp and/or medusa phases, are radially symmetrical, usually with tentacles and contain stinging cells produced by the animal itself. Examples of Cnidarians include a range of animals from corals and sea anemones to hydroids and marine stingers. The three classes of marine stingers that can inflict a painful sting include the Class Hydroza, Class Scyphozoa and Class Cubozoa. The term 'box' jellyfish can often confuse people as it is a general term used to describe Cubozoan jellyfish, including Irukandji, the Jimble and Chironex fleckeri (commonly known as 'box jellyfish'). Whilst these are the individuals pose the greatest threat, within the other two classes are the blue bottle and hair jelly which can cause much discomfort. The intensity and severity of the sting from a marine stinger varies with geographical location and a the health and fitness of the victim."