This Saturday's Liffey Swim is going ahead.
It follows concerns over the result of water quality tests following a recent overflow into the river.
Water in the river is extremely dirty after an overflow from a sewer network.
Samples were taken on Wednesday and Thursday and the results show the quality is well below the standards for bathing areas.
The results are "exceptionally poor, and significantly exceed the maximum permitted levels for designated bathing waters".
Dublin City Council has notified the HSE and event organisers and say it's hoped the river will be safe to swim in by tomorrow.
However, they said the final decision rests with organisers - who've now confirmed the event will proceed.
The council, meanwhile, said that " a number of tidal cycles will have taken place prior to the Liffey Swim".
It also explained that the ESB "will increase flows in the Liffey prior to the event to further dilute any residual contaminants".
"It would, therefore, be hoped that the river water quality will have improved significantly by the time of the event".
600 people are supposed to take part in the 100th anniversary of the race tomorrow.
Those taking part are being asked to read the HSE's advice.
