The man who died after his car plunged into a Southland river was a "typical Kiwi bloke", his brother says.

Te Iwiroa Smith, 44, of Curio Bay, was driving with a 40-year-old male passenger when the car entered Mataura River, 45km southeast of Invercargill, at 5.30am on Monday.

The passenger escaped -- but took more than seven hours to report the crash to police.

Te Iwiroa's brother Rata Smith, a former Southland Stags player, slept the night by the river until Smith's body was recovered.

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Rata told the Herald he would remember his brother for his love of the outdoors and friendly nature.

"He was always friendly and chatty. He'd talk to anyone.

"He was a typical Kiwi bloke. He enjoyed hunting and diving; anything in the outdoors."

He loved children, though he never had any of his own, Rata said.

"He was a family man. He enjoyed children and treated his three stepchildren like they were his own.

"He was always keen to do things with them; hunting and that sort of thing."

Rata said he didn't know the passenger and hadn't attempted to make contact with him.

Investigators won't say why it took seven hours for the man -- who didn't require medical attention -- to contact police.

Police have launched a serious crash investigation to determine how the car entered the river.

The funeral for Smith will be held at his home in Tokanui on tomorrow afternoon.