Dangerous jellyfish and dirty water are causing problems for swimmers on six Dublin beaches.
Lion's mane jellyfish, capable of inducing anaphylactic shock, were discovered on Sandycove beach by Dun Laoghaire/Rathdown Council staff.
The Council has now placed warnings at Killiney, Sandycove and Seapoint beaches on the advice of Irish Water Safety and the Irish Coast Guard.
Swimmers have also been warned about poor quality water on Burrow and Claremont beaches in Sutton and Loughshinny beach in the north county.
Seventeen lion's mane jellyfish were removed from the water at Sandycove. This species, which can cause "excruciating pain", has hundreds of long, hair-like tentacles.
The sting can cause nausea, vomiting and respiratory distress. Bathers are being advised not to enter the water at these beaches.
Red warning flags have been erected in the lifeguard- patrolled areas and swimmers will be advised of potential dangers.
Meanwhile, a spokesperson for Fingal County Council said that the two Sutton beaches and Loughshinny beach had not been closed but that the council was issuing "precautionary notices".
She explained that poor quality water had been found at the mouth of outflow pipes carrying surface-water to the three beaches.
The beach water itself was not contaminated and this was why the beaches remained open and the warning notices had been placed at the mouth of the outflow pipes.
Council staff would review these notices once they received results from further tests.
A bathing ban was lifted at Dollymount beach yesterday by Dublin City Council, which had previously lifted bans at Sandymount and Merrion beaches.
Dun Laoghaire/Rathdown Council had just lifted a water quality bathing ban at Killiney and Sandycove beaches when the jellyfish alert was raised.
Beaches at White Rock and Corbawn are still open for bathing.
Meath County Council has lifted the ban at Bettystown Beach .
In Fingal, beaches that have been passed for swimming include those at Portmarnock and Malahide, Tower Bay and Portrane, Donabate, Skerries South and North and Rush South and North beaches.
Many of the bans were introduced this week when levels of bacteria rose after a weekend of extremely heavy rain.
Irish Water Safety has advised people not to get stung when helping others who have been affected by jellyfish.
Attached tentacles should be removed with a gloved hand, stick or towel and, if none of these are available, the tips of the fingers. The area should be rinsed with sea-water. If patients are suffering from swelling, breathing difficulties, palpitation or chest tightness they should be urgently taken to the nearest emergency room.