Seventeen dangerous and severely stinging jellyfish, known as lion's mane were removed by Dun Laoghaire Rathdown County Council from Sandycove Beach today.
The jellyfish have hundreds of long hair-like tentacles and can cause a very severe sting to bathers. Irish Water Safety chief executive John Leech said the jellyfish can be "very venomous and very dangerous".
The council said it had erecting warning signs on three beaches in south Dublin, Killiney, Sandycove and Seapoint on the advice of Irish Water Safety and the Irish Coast Guard.
The signs advise bathers “not to enter the water due to a presence of a specific jellyfish whose sting can be dangerous and cause serious symptoms including nausea, vomiting and respiratory distress,” the council said in a statement.
The council said red warning flags have been erected in the lifeguard patrolled areas and swimmers will be advised of potential dangers.
The jellyfish were spotted by employees carrying out their normal cleaning duties, the council said. Photographs of the creatures were taken before their “safe disposal”, the council said.
Mr Leech said the jellyfish can be as venomous as the notorious Portuguese man o’war (which is not technically a jellyfish).
The pain from the sting is “excruciating” and some people can get anaphylactic shock in addition to sting pain. The anaphylactic shock from the sting can result in death from heart failure, he said.
He said lifeguards in many parts of the country are doing jellyfish patrols every half hour on a rescue board or boat. He urged people only to swim in lifeguarded areas for this reason.
According to Irish Water Safety the lion’s mane jellyfish (cyanea capillata) can reach a bell diameter of 2 meters but are normally much smaller. They are divided into eight lobes and eight clusters with up to 150 tentacles each, it said. The colour of the jellyfish varies from deep red to yellow.
It is the largest of the species found in the Irish Sea. The sting can produce blisters, irritation, and muscular cramp and "may even affect respiratory and heart function", according to Marlin the The Marine Life Information Network. The jellyfish can sting long after they are stranded on a beach.
Last week Irish Water Safety warned that the lion's mane jellyfish had been spotted at Dublin bay in Sutton. So far this year there have been sightings in Clare, Louth, Belfast and Dublin.
High temperatures, prevailing westerly wind and north Atlantic current meant te potentially dangerous jellyfish were likely to appear on more beaches in the coming weeks, it said.
In recent weeks a girl was rushed to hospital from Barleycove in west Cork after an allergic reaction to a jellyfish sting.
Irish Water Safety has published first aid guidelines on treating people with jellyfish stings, which were developed by the Jellyfish Action Group.
It advises people not to get stung when aiding others. Attached tentacles should be removed with a gloved hand, stick or towel and if none of these are available the tips of the fingers. It urges people not to rub the affected area as this may result in more venom release. The area should be rinsed with sea-water – not with fresh water, vinegar, alcohol or urine, it says.
A dry cold pack should be applied to are stung area ( this can be cold pack or ice inside a plastic bag and wrapped in a t-shirt), it advises. It urges people to seek medical attention if they experience anything more than minor discomfort. IF patients are suffering from swelling, breathing difficulties, palpitation or chest tightness they should be urgently taken to the nearest emergency room, it says.