Rory Smith (19) was reported missing at 10.30pm on Friday.
His body was found washed up at Karaka Bay near Wellington on Saturday morning.
It was initially reported by authorities that the teenagers had gone swimming - but Smith's father today told the Herald that was not the case.
Wayne Smith was not ready to speak about his son, but he did want to make sure people knew the truth about his death.
He explained that Smith and his friend were walking through a park near Belmont School in Lower Hutt when tragedy struck.
"That park is partially lit by the motorway lighting and is quite visible at night," Wayne Smith said
"The river came up so far that it cut across the path, that's where they got into difficulty, in a corner of the park that wasn't well lit."
Wayne Smith said his son's mate slipped from the path into the water.
"He was in the water... he was holding on to a tree," he said.
"Rory came straight through to him and he fell into a massive hole."
Smith was swept away and his friend managed to get to safety and raise the alarm.
At the time the Hutt River was still very high with a fast-moving current.
An extensive search was carried out but Smith could not be found.
In a Facebook post announcing his sad news, Wayne Smith said his son's death was "just a stupid bloody accident".
Funeral arrangements were yet to be finalised, but the family hoped to farewell Smith on Thursday or Friday in Lower Hutt.
