Bathers are being advised to stay out of the water at Sandycove in Dublin due to the presence of dangerous jellyfish.
The warning comes ahead of an Ironman event on Sunday, which involves a 1.9km swim from Sandycove Point. The event is due to start at 6.50am.
In a tweet, the event’s organisers said athlete safety was “paramount” and that they would monitor the situation.
“We are aware of the jellyfish situation in Sandycove,” they said.
“Athlete safety is paramount. We will continue to monitor and take action if necessary.”
The warning was issued by Dún Laoghaire-Rathdown County Council on Wednesday.
“We have raised the red warning flag in Sandycove and erected signs warning swimmers of the presence of jellyfish in the water and washed up on the beach,” it said.
The species was identified as the Lion’s Mane jellyfish, which is the largest of the species found in the Irish Sea.
“Bathers are advised not to enter the water due to the presence of these jellyfish, whose sting can be dangerous and cause serious symptoms, including nausea, vomiting and respiratory distress,” the council said.
Last month, John Leech, of Irish Water Safety, said the Lion's Mane jellyfish had become more plentiful in Irish waters, with reported sightings along the east coast.
Sting
The jellyfish have hundreds of long hair-like tentacles and can give bathers a very severe sting.
The sting can produce blisters, irritation, muscular cramp and may even affect respiratory and heart function.
Some people can also suffer from anaphylactic shock after being stung.
This anaphylactic shock can result in death from heart failure.
The jellyfish can reach a bell diameter of 2m, but are normally much smaller.
They are divided into eight lobes and eight clusters. The colour of the jellyfish varies from deep red to yellow.
The jellyfish can retain its sting long after it is washed up on a beach.
Seventeen of the jellyfish were removed by the council from Sandycove Beach in August 2014.
