"We salute our Ngati Dread RIP Willie Collins!" Dwayne Russell wrote.
"Can't believe you are gone my brother."
Mr Collins' family also posted several touching tributes online today.
According to family members Mr Collins, known as Tou, was born in 1976, and was described as a strong man who helped guide his clients.
A family member said he spent parts of his childhood in Auckland and Taupo, as well as Wellington.
"Brother you were supposed to wait for me," Reetah Collins wrote.
"...You were my pride and I knew you were the strong one now you've left me and I'm too far from you. I love you bro Willie Collins will miss you."
Supporters of Mr Collins' gym were also paying tribute to the personal trainer on Facebook.
"Willie was a true gentleman with a huge heart, passion and love," one wrote.
Ngati Porou East Coast rugby union paid homage to Mr Collins.
"Another Wellington Rugby legend gone to soon. A man making a difference in people's lives," the union wrote online.
In 2013, Mr Collins taught crossfit, boxing technique, healthy nutrition and mental strengthening, Whitireia Newswire reported.
In 2001, Mr Collins was among the few players without direct Ngati Porou whakapapa or relations playing for the club.
He also played for Ngati Porou East Coast in 2004, after "having completed club commitments in Wellington".
A fan of the club said on Facebook today the PRFC flag was flying at half-mast.
Mr Collins had been in the health and fitness industry for over 20 years, according to the Limitless Fitness website.
Apart from playing rugby for Petone and Ngati Porou East Coast, Mr Collins played rugby league and sevens.
He was also a keen boxer.
"I won a national title in amateur heavyweight boxing and turned professional in 2010," his website added.
He said his clients over the years had included clinically obese people "with significant health issues" as well as athletes.
"My goal is to coach and train people to not only meet their goals, but to exceed them to maintain their healthy lifestyle and be an inspiration to others," Mr Collins wrote.
Petone Rugby Club (PRFC) said Mr Collins played for both the senior 1st and premier teams.
The club extended its condolences to Mr Collins' family.
On the club Facebook page, PRFC said the Collins family had long been "stalwarts" at the club.
The club said Mr Collins' service would be held on Wednesday evening, with a funeral held the day after, Christmas Eve.
Start times and venue were yet to be confirmed.
The drowning comes just eight days after another diver was found dead in the area.
It is the second tragedy to hit the Collins family this year, after Jerry Collins died in a car crash in France, along with his wife Alana Madill.
The couple's baby daughter Ayla survived the crash with serious injuries, and is being raised in Canada by Ms Madill's family.
