Video: Mum delivers heart-rending oration at funeral of five of her family members
Louise James choked back tears as she addressed those who had packed Holy Family Church in Derry today.
There was loud applause when Ms James said: "We will be eternally grateful to Davitt Walsh, for without fear for his own life and safety you entered the Lough Swilly to save my Rionaghac.
"I will be forever grateful to you. Thank you so, so much."
Sean McGrotty, 46, died alongside eight-year-old Evan and 12-year-old Mark, Ruth Daniels, 57, and 14-year-old Jodie Lee Daniels when their SUV sank after sliding off a slipway in Buncrana, Co Donegal.
Ms James, who had been away for the weekend, said four-month-old Rionaghac-Ann, the sole survivor of Sunday's accident in Lough Swilly, is her only reason to go on living, having lost her partner, two sons, her mother and sister.
She also expressed a deep gratitude to Francis Crawford, the man who had raised the alarm, and the emergency services who battled to resuscitate her family members on the pier-side.
"We as a family would like to take this opportunity to thank all those involved in the tragic events of Sunday evening," she added.
The Catholic church, less than a mile from the family home in the Ballymagroarty area of Derry, was filled to capacity, with thousands more people spilling out into the car park and surrounding streets.
Among those in attendance were Northern Ireland's Deputy First Minister Martin McGuinness, Foyle MP Mark Durkan and SDLP leader Colum Eastwood, as well as Stormont Environment Minister Mark H Durkan.
Earlier mourners heard how little Evan had spoken to his mother on the phone minutes before the car dived into the water.
He told her: "Mammy, I miss you so much.
"I am going to give you the biggest, tightest hug you ever got, when I see you again."
There was more applause when parish priest Father Paddy O'Kane asked the congregation to salute the bravery of Mr Walsh, a former footballer who swam out to help the stricken family.
It is understood the Audi Q7 lost grip on a thick blanket of algae coating the slipway and slid into the water.
Mr McGrotty handed his baby to Mr Walsh through the broken driver's side window just moments before the vehicle sank.
Father O'Kane told the funeral service: "Davitt, today we salute you as our hero."
The priest also revealed Ms James' words to Mr Walsh and his girlfriend, Stephanie Knox, who stripped the infant and warmed her at the shore, when they met at the parochial house on Tuesday.
"Don't blame yourself that you did not do more - we are so grateful for what you did," the priest said Ms James told the couple.
"It could easily have been seven deaths, not five."
Father O'Kane revealed that when the grieving mother also gave Mr Walsh her baby to hold at the meeting, she opened her blue eyes, smiled up at him and gave a big yawn.
Mourners heard that the family has suffered other losses, with another of Ms James' sons, Joshua, only living for 17 hours and Mr McGrotty's younger sister, Ann, dying from cancer last July.
"You are just going to have to wait a little longer until you get that tight hug promised to you from Evan," Father O'Kane told Ms James.
Mourners also heard that the mother had raised £16,000 for a charity which helps people with muscular dystrophy, including doing a tandem parachute jump from 14,000ft (4,267m), after Evan was diagnosed with the condition.
Investigations into the cause of the tragedy are continuing, with the pier shut to vehicles.
Tributes were paid to each of the victims during the service.
Schoolteachers recalled vibrant, model pupils in Jodie Lee, Mark and Evan, while Mr McGrotty's brother Jim also spoke movingly about a devoted father and Mrs Daniels' son Joshua remembered a much-loved mother.
Bishop of Derry Donal McKeown, who visited the family, told the service that love and life are stronger than death and the bitterest tragedy.
"These have been sombre days, not only in this city but right across this island," he said.
"The banks of daffodils seemed to wave naively in the face of the horror that happened in a few minutes on an apparently harmless pier at Buncrana. And the news of the awful events in Brussels underlined just how fragile life can be."
Bishop McKeown also praised the response of the community in Derry.
The service was also attended by Church of Ireland Bishop Ken Good, Commandant Louise Conlon, representing Irish President Michael D Higgins, and Kieran Carey, representing Acting Taoiseach Enda Kenny.
Earlier he met the family with Northern Ireland First Minister Arlene Foster.