Police said the incident occurred on Sunday afternoon.
The person is understood to have been rafting and passed away at the scene.
A WorkSafe New Zealand spokesperson confirmed an investigation had been launched into the weekend rafting fatality on the Clarence River.
"We cannot comment further while our work is ongoing to establish the circumstances and parties involved," the spokesperson said.
It comes after the manager of Clarence River Rafting, Ben Judge, earlier said news of the death was very sad, saying the incident had nothing to do with his company or any of the other three operators who have concessions on the river.
"It would look like it was not a commercial raft trip, it was a private raft trip," Judge said.
"I can’t 100 per cent confirm that but I can absolutely, 100 per cent confirm it wasn’t Clarence River Rafting," said Judge, who said he had been in communication with the other companies who confirmed the incident did not occur on one of their river trips.