'Humble and shy': Family members remember teen who died while swimming on Sydney's Northern Beaches

The mother of Ivan Korolev, the teenager who drowned at Freshwater beach on Sydney's Northern beaches on Saturday night, has remembered her son as humble.

Anna Kolotukhina and her family thanked the search teams who found the 18-year-old and the local community for surrounding them following his death.

Kolotukhina described her son as humble and shy, saying he achieved everything he put his mind to.

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"I had a deep and meaningful relationship and understanding so apart from being my son he was my close friend," she told 9News.

Ivan was about to start his studies at the Australian Catholic University to become a physiotherapist.

"The sheer happiness he went through in the last few weeks was just unbelievable," his mum said.

He was highly skilled at parkour, rock-climbing and martial arts - hobbies which drove his passion for fitness and health.

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Mystery still surrounds exactly how the teenager drowned while he was swimming with his friends.

"I was told he swam within a short distance of his friends ... they were chatting ... having fun and his last words were 'I'm so relaxed now I'm ready to fall asleep'."

A GoFundMe page has been set up by a family friend to help with funeral and tribute costs.