Here's one for Jilly in Menton

Trinity Beach, just north of Cairns. There's no swimming on this part of the beach between November and May because that's "stinger season". The main two to worry about are the Box Jellyfish and the Irukandji Jellyfish.

The Box Jellyfish can administer a sting that inflicts searing pain and leaves prominent scares, and if severe enough can be fatal.

The Irukandji are much smaller than box jellyfish, and inhabit a large sea area that includes the Great Barrier Reef and beaches.

The sting is only moderately painful and scarring is minimal, but approximately 30 minutes after the sting the patient develops severe back and abdominal pain, limb or joint pain, nausea and vomiting, sweating and agitation. It too can be fatal.

Many of the popular beaches have "stinger nets" enclosures designed to keep them out and where swimming should be safe. When we snorkelled on the reef we wore lycra top to toe stinger suits. They even have coverings for your hands and head.

Many beaches in northern Queensland have bottles of vinegar on hand in order to provide first aid treatment. Here's what wikipedia says about vinegar treatment:

Following a sting, vinegar should be applied for a minimum of 30 seconds. Acetic acid, found in vinegar, disables the box jelly's nematocysts that have not yet discharged into the bloodstream (though it will not alleviate the pain). Vinegar may also be applied to adherent tentacles, which should then be removed immediately; this should be done with the use of a towel or glove to avoid bringing the tentacles into further contact with the skin. These tentacles will still sting if separate from the bell, or if the creature is dead. Removing the tentacles without first applying vinegar may cause unfired nematocysts to come into contact with the skin and fire, resulting in a greater degree of envenomation. Vinegar has helped save dozens of lives on Australian beaches.