Mourners were told how the “fun-loving” young man “lived every day like it was his last”.
Police confirmed that Mr Ó Faoláin entered the water in the lake shortly after 11pm on Saturday and got into difficulty.
A search team located his body on Sunday. They confirmed his death is not being treated as suspicious.
The 21-year-old from the Brantry area of Co Tyrone was one of six siblings and a twin to his sister, Dearbhla.
A funeral notice said he was the beloved son of Shane and Fiona (née Gildernew) and was also described as the dear grandson of Phelim and Geraldine Gildernew and Eileen and the late Patsy Fullen RIP.
His funeral Mass took place on Thursday in St Joseph’s Church, Caledon where mourners filled the pews to pay respects to the young man who was described as “generous, hard-working, confident, fun-loving and sociable”.
His father, Shane, said how “a massive part of our jigsaw is now gone”.
“Fiachra was an amazing young man and Fiona and I were very blessed to call him our son,” he told those at St Joseph’s.
“We had 21 amazing years full of highs and low and everything in between and we wouldn’t change one single thing.
“Over the last few days we have realised just how much he was and still is loved by so many people; we can’t thank everyone enough for their support and prayers we have felt.
“A massive part of our jigsaw is now gone; life will never be the same, but we know he will walk beside us every day of our lives and we look forward to the day when we can hold him close.
“Rest easy, my gorgeous beautiful boy.”
The priest conducting the service told those in attendance how Fiachra “touched the lives of everyone he met”.
“He was a man who made time for people young and old and who in turn was deeply loved by his family and many friends as well as his work colleagues and teammates,” he said.
“Over the years he enjoyed hurling – though he wasn’t very good at it – but would add to the entertainment!
“Also, the football, the farming, the boxing, keeping fit, swimming, fishing and the push up competitions that he always won,” he added.
“He had a real passion for life and lived every day like it was his last forever telling his family how much he loved them.
“His infectious smile and ability to make them laugh will be long remembered and cherished.”
The family also told of how Fiachra was “full of sincerity and impulsivity” adding that he “enjoyed life and added so much to other people’s enjoyment of life as well”.
“In the days ahead, the family will no doubt look back on a life well-lived,” the priest said.
Fiachra was also the nephew of Sinn Féin politicians Michelle and Colm Gildernew, who thanked those who paid tribute to Fiachra.
Former Sinn Féin MP Michelle Gildernew said earlier this week “there are no words” after the tragic death of her nephew at the weekend.
Mrs Gildernew posted on X on Tuesday: “There are no words. I’ve heard that so many times and there aren’t, but there are actions. Every hug, every handshake, every message & phone call, we have been comforted and supported. Thank you, from the bottom of my heart, for your care. #Fiachra In ár gcroíthe go deo.”
Ms Gildernew also thanked the large numbers of people from across Ireland and beyond who extended their condolences over the past week.
“Our hearts are broken following the death of our wonderful nephew Fiachra. He was a funny, impulsive, kind and generous young man who will be missed so deeply by all of us,” the Sinn Féin candidate for the Midlands North West in the Republic’s European election said.
“My thoughts are with his parents and brothers and sisters who are experiencing the most unimaginable grief.
“I want to thank all of those people, from across Ireland and around the world, who have been in touch to send their sympathies and prayers to us. Your support means so much to the entire family at this time.”