McCarthy, who played in the AFL from 2014-2020, was found dead at Lake Coogee in Perth on Thursday evening.
"The death is being treated as non-suspicious," WA Police said in a statement, adding a coronial report would be prepared.
The West Australian-born footballer played 70 AFL games and kicked 99 goals for his two clubs, who both expressed shock and sadness at his passing.
"His death is tragic and to all of his family, friends and teammates, we extend our deepest condolences," Fremantle's chief executive Simon Garlick said.
"Cam was a kind and easy-going person at the club and he was someone who had a habit of making people smile and laugh.
"His talent was undeniable and he loved his footy."
GWS chief executive David Matthews said news of McCarthy's death had a "profound impact on many current and former Giants players and staff".
"Cam had great energy and was a much-loved member of our club for the seasons he was here," Matthews said.
"He was very popular and a bright footballing talent. We extend our deepest sympathies to the entire McCarthy family and his many friends."
AFL chief executive Andrew Dillon said he was deeply saddened by the death of McCarthy, who was drafted by GWS with pick No.14 in 2013.
He played 21 games for the Giants before leaving the Sydney club at the end of the 2015 season, citing mental health issues and homesickness.
After failing to engineer a trade to Fremantle for the 2016 season, McCarthy stood out of AFL football before being picked up by the Dockers.
The talented forward played 49 games for Fremantle in four seasons from 2017 before being delisted in what the club and player described as a mutual decision at the end of 2020.
During his last season in the AFL system, McCarthy was diagnosed with epilepsy after collapsing at training.
AFL Players Association chief executive Paul Marsh also offered support to McCarthy's family and friends.
"This is a terribly sad time and we will make available whatever services and support Cam's family, former teammates and his two football clubs may need during this tough time," Marsh said.
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