Kohu's friend managed to swim to the other side and climb up an embankment and also call for help.
But Kohu was unfortunately lost.
On the night Kohu went missing, the police boat, Waikato Westpac Rescue Helicopter and the Fire and Emergency drone all carried out searches, to no avail.
The police national dive squad also joined the search in the days after his disappearance.
His cousin, Te Hikuwai Kohu, earlier told the Herald she did not understand why he was swimming at that hour.
"He was really smart and he was a black belt at 11 or 12, he used to do karate growing up, he was smart as.
Members of the Police National Dive Squad enter the Waikato River near Hamilton Gardens to search for Kayne Kohu who went missing in the water on Sunday night. Photo / Mike Scott
"He was pretty mature for his age, he didn't drink, well I thought he didn't drink."
To hear that he was down swimming at the river on Sunday night was a shock, she said.
"And he knows that he's not allowed in the river."
She said her cousin should have known that as his nan - victim advocate and psychotherapist Hinewirangi Kohu-Morgan NZOM - had always told him to steer clear of it.
Kohu, originally from the Bay of Plenty, had been working at Camarosa Restaurant on the outskirts of Hamilton, with renowned chef Andrew Clarke.
Kohu had followed in his father's footsteps and become a chef after initially dabbling in the plumbing trade.
"He always cooked for us. He taught himself, he didn't have a qualification or anything he just learned from the bottom like from being a dishwasher and worked his way up," Te Hikuwai said.
