A 27-year-old man, Noel Quinlivan from Scanlan Park, Castleconnell, died in hospital yesterday afternoon after firemen had rescued him at around 7am in and operation that took more than two hours.
Three others were brought safely to shore after what witnesses described as a perilous and challenging river rescue.
Mr Quinlivan had been in the river for three hours and been trapped by a tree, which fell and lodged in the river, during recent floods.
Gardaí, under Supt Derek Smart of Henry St, are conducting an investigation into the death. The Marine Casualty Investigation Board (MCIB) will carry out a separate inquiry.
The deceased was one of four men in their 20s and 30s who were thrown into the rapid flowing river after a boat capsized.
It is believed they got into a boat at a local boat club at around 4am after attending a house party.
Three specially trained members of the Limerick Fire Service spent more than two hours in the raging waters, trying to extricate Mr Quinlivan from the tree where he got trapped.
In the meantime, Castleconnell boat club said it had not given permission for any boat to be used.
Mr Quinlivan died at University Hospital Limerick.
Throughout the rescue, only his head was visible above the water and his body temperature was at a critical level when removed from the river around 7am.
The men had gone out on the river in a 16ft fibreglass launch.
Within minutes they lost control of the boat and it overturned, throwing all four into the water.
Three were close to the river bank and one managed to make a 999 call at around 4.20am.
Mr Quinlivan was swept out into the middle of the river and he became entangled in the branches of a tree which had been carried down the river in the recent floods. The Coast Guard regional control centre alerted all the rescue services.
Four fire engines from Limerick fire service rushed to the scene along with Killaloe Coast Guard, gardaí, Limerick Marine Search and Rescue, and local people.
During the rescues, the Shannon 115 helicopter trained its high-power search lights on the scene.
A spokesman for the fire service said: “This was a very perilous and evolving situation and all who were involved in the rescue did a marvellous job in getting the four men to shore. The river was like a rapid.”
Three of the men were rescued within a relatively short period of time and one had a serious leg injury.
Mr Quinlivan was located mid-stream, wedged in a large tree. One source said: “All that was visible was his head.
“Three highly-trained swiftwater rescue technicians (SRT) from the Limerick fire service swam to the area where the man was trapped.
“The three SRTs had to work in very dangerous and almost impossible conditions. Due to where he was in the water, it was not possible to get a boat near him and they had to get through to the trapped victim who was caught in the branches of the tree.
“The fast-flowing river made it a most dangerous operation. However, after some time they managed to get him free and into one of the rescue boats which brought him to the river bank. CPR was administered to him and it was obvious he was in a critical condition. The other three had by this time been brought to University Hospital Limerick.”