Current conditions are said to be 'ideal' along Irish coasts for a jellyfish which is known to cause painful stings, cramps, nausea, and headaches.
The lion's mane jellyfish is set to increase in number along beaches and shallow waters on eastern costs over the next couple of weeks of September.
The HSE describes the jellyfish species as the "most serious" jellyfish in Irish waters.
In a statement by Fingal County Council, bathers are urged to be "extra vigilant on all beaches where lion's mane jellyfish are found."
People are also advised to steer clear of dead lion's mane jellyfish as their venom can stay in their tentacles for a few days.
"With so many long trailing tentacles there is a chance you could still get stung, even when you try not to swim near them", said Fingal County Council.
"Also, fragments of the lion's mane jellyfish's tentacles that break off in the water will sting you, even if they're no longer attached to the jellyfish."
Those who receive severe lion's mane jellyfish stings are advised to seek urgent medical attention.
Any attached tentacles should be removed with a gloved hand, stick or towel, while people should not rub the affected area as that may result in more venom release.
People are advised to rinse the affected area with seawater and then warm to hot water at home and to apply a dry cold pack, while you should never rinse the sting with fresh water, vinegar, alcohol, or urine and do not put on a tight bandage.