A 27-year-old Armagh man, named locally as David Warnock, died after he was pulled from the water on Thursday afternoon.
Another man, believed to be 60, remains in a critical condition in hospital.
A major multi-agency operation to find the third man resumed at first light on Friday but Damien Delaney from Lough Ree RNLI Lifeboat Station said the search had almost been exhausted and that forecast gales could hamper the operation.
Most of the boat's contents have been recovered along the east shore of the lough.
"Certainly within the range of the debris, the most likely places he could have been if still afloat, we've walked most of the shoreline where he may have got ashore," he said.
The search may well have to become, rather than a search and rescue, a recovery operation.
Damien Delaney, Lough Ree RNLI
Local politicians have expressed shock at Mr Warnock's death.
UUP Craigavon Deputy Mayor Colin McCusker, a relative of the man, said: "We have a massive family circle and this is a young man of less than 30 with his life ahead of him.
"As a family we are devastated. We are just in limbo because they are three hours from home and we are just trying to prepare for what we need to do over the next few days. We're just in shock at the minute."
DUP Upper Bann MP David Simpson also knows some of the families caught up in the tragedy.
"These men set out to do something they loved. They wanted a short break where they could relax and enjoy their sport," he said.
"No one anticipated that their journey to Lough Ree would result in this tragic and heartbreaking news.
"In such a situation no words can sum up feelings of the families. I can only assure them of my prayers and the support of the community in Portadown."
The lake is very beautiful but it is obviously very dangerous and it is very sad when you look across it and you think that somebody lost his life on it last night.
Cllr Gabrielle McCusker, Mayor of Athlone
The three had set off for Carnagh from Hodson Bay and were part of a group who had travelled to the area with members of the Portadown Pikers angling club.
It is understood they intended to camp in the Carnagh Bay area for the weekend and fish on the lake.
Conditions were believed to be poor on Thursday afternoon when the party of six set out in two boats, although one turned back to shore.
They were using two 15ft Dell Quay Dory flat-bottomed vessels which were heavily laden with fishing and camping gear, much of which was found strewn across the lough during the search.
Two of the men were rescued by lifeboat crews and taken to hospital in Ballinasloe, Co Galway on Thursday after a local person raised concerns about the deteriorating conditions - but Mr Warnock did not survive.
Eyewitness Tommy Byrne watched the tragedy unfold as he worked on his camper van at the lough harbour. He described the scene of the lifeboat's arrival with the first of the rescued men.
"Everybody was rubbing him trying to get his circulation going, giving him O2 [oxygen], giving him CPR," he said.
Mr Byrne said they wrapped the man in a duvet and placed him in the back of his van until the ambulance arrived.
The lifeboat then set off to locate the second man.
When he was brought to the shore, Mr Byrne said: "It didn't look good and he was in a bad way."