A man is in a serious condition in hospital and another is in custody following a dramatic rescue operation on the Liffey after they deliberately jumped into the water while drunk.
The incident happened in full view of shocked tourists in the middle of the afternoon.
Members of Dublin Fire Brigade responded to reports of a man in serious difficulty near Wellington Quay.
It is believed that the men, of Eastern European origin, decided to take a dip after they had been drinking on the boardwalk near the Ha'penny Bridge.
After only a short time, one of the men got into difficulty and emergency services were called.
Gardai confirmed that one man was arrested for intoxication at the scene after he climbed out of the river with the aid of a ladder.
The other man was taken to St James's Hospital where last night he was in a serious but non-life threatening condition.
The incident happened shortly before 3pm.
A passer-by told the Herald that gardai alerted the fire brigade after they were unable to reach the second man.
"The guards threw him a buoy to help him keep afloat but he seemed in a bad way," said the witness. "When the rescue boat reached him, they gave him CPR and wrapped him in one of those body-heat bags.
"He was taken up the ramp where the Discover Ireland ferry comes in and taken away in an ambulance."
A brigade spokesman said: "An injured man with low-levels of oxygen was taken aboard a lifeboat at around 3pm."
Sources said the men "appeared to have been intoxicated" before entering the water and are understood to have been seen drinking on the boardwalk throughout the afternoon.
"It appears they decided, for whatever reason, to go for a swim," a garda source said.
"One man is still currently being detained at Pearse Street Garda Station."
The incident happened in one of the capital's busiest areas for tourists, and it is understood that dozens of overseas visitors were among the crowds who watched.
An American couple said they were "surprised" at events.
"I wouldn't have thought drinking out in the open like that would have been tolerated, but I guess the police can't be everywhere," said the woman.
"Aside from themselves, it doesn't seem like the men hurt anyone."
A Failte Ireland representative said that while it was "disappointing" that visitors had witnessed such as incident, "the vast majority of tourists to Ireland have nothing but positive experiences".
"Tourism to Dublin is booming at the moment and often we're told that people feel very safe walking its streets," he said.
"Ireland is still rated as among the safest places to visit, and 96pc of people who come here say the same."
Dublin Town CEO Richard Guiney said "such instances shouldn't spoil people's perception of the capital".
"The city is safer now than it was five, 10 years ago. The gardai have done a wonderful job of cracking down on the anti-social elements."