Simon Lawn of Ahaura Helicopters said it had been a traumatic day for the men.
"They were pretty upset that they couldn't save both of them but I said they saved one person out there and that's the main thing."
It is understood the two in the boat were not wearing lifejackets or wetsuits.
A police spokeswoman said officers were called to the scene, about 1 km upstream from the William Stewart Bridge, about 2.25pm.
Police confirmed one person was rescued and treated by ambulance.
"We are still searching for one other person and the search will resume in the morning," the police spokeswoman said.
Emergency services will resume searching on Saturday morning.