Box Jellyfish Near Samui: Warning and How to Swim Safely

Box jellyfish were confirmed near Samui and Phangan in August 2025; an expert advised swimming only inside netted zones.

Box jellyfish were confirmed in the sea near Koh Samui and Koh Phangan in early August 2025. A public warning was issued by Dr Thon Thamrongnawasawat, deputy dean of the Faculty of Fisheries at Kasetsart University, according to the Pattaya Mail on 5 August 2025. He asked beachgoers to swim only in areas protected by nets.

What the warning said

The advice in the report was short and clear. Swimmers should stay inside the netted zones that some beaches provide. They should also avoid going into the sea at dusk or at night.

The Pattaya Mail reported that local marine and coastal resources officials were monitoring the situation. Warning signs were being placed, and beaches considered higher risk on both islands were being watched. The article did not name specific beaches and gave no figures for stings or injuries.

First aid as described in the report

The report stressed that fast action matters after a sting. The steps it gave were:

Pour vinegar over the stung area for at least 30 seconds. Household vinegar with 4 to 6 per cent acetic acid is the type mentioned.
Do not use fresh water.
Do not put ice on the area.
Do not rub the wound.

The reason given is that fresh water, ice and rubbing can cause more venom to be released. This is general safety information from a news report and not medical advice. After any serious sting, get medical help immediately and tell hotel or beach staff, who can call local emergency services.

Keeping the risk in proportion

The warning did not close the sea. The report describes no ban on swimming, only advice on where and when to swim. It means that a dangerous species has been confirmed in these waters and that a few simple habits lower the risk. Reading the warning signs on the beach, and following them, is the first of these habits.

What it means for your stay

If you are travelling with children, choose beaches or hotels with a netted swimming area when one is available, and read any warning signs when you arrive. Keep a small bottle of vinegar in your beach bag. Avoid night swims in the sea, which are best replaced by a swim in the pool.

Ask local staff if there have been recent sightings on the beach you plan to use, and choose another beach or the pool if there have.

Health and safety advice can change, so check current official guidance from the Thai authorities before you travel. If you would like a private pool for worry-free swimming, have a look at our villas for rent in Koh Samui.