Paul Gallihawk, 34, failed to finish the initial swimming part of the race at Leybourne Lakes and was reported missing after he did not arrive to collect his bike for the cycling stage.
The cause of his death remains unclear.
His girlfriend Hayley said: "He was the most amazing and thoughtful partner. I loved him to bits and always will."
"He was incredible in every way and he always put others before himself," she added.
In a statement, the family said: "[Paul] had such a caring nature and will be sadly missed by all the family, extended family and friends.
"Paul was a brilliant son and brother to Nick - he would do anything to help anyone and would always put them first."
His friends also issued a statement: "Many of us have known Paul since we went to school together and we are all completely heartbroken.
"He was a genuine and honest man - he was the funniest person in the world."
The triathlon event was organised by Ocean Lake Triathlon, who said: "We are shocked by what happened."
The triathlon club, based at Leybourne Lake Country Park and Simon Langton School in Canterbury, organises a series of six sprint distance races.
Mr Gallihawk had been missing since a 750m swim at the start of the triathlon.
He had written on his JustGiving page that he was competing to raise money for King's College Hospital in London, which had looked after his father. Since his disappearance was announced, donations on the page have risen to over Â£6,000.
One donor wrote on the site: "Paul, you always had a smile and a laugh about everything, and a great teammate playing for Lenham. An absolute gent and our thoughts are with your loved ones."
Tributes have been paid to a triathlete whose body was found after he disappeared during a race near Maidstone on Saturday.