Detective Senior Sergeant David Harvey said that while the man had no obvious injuries, it was still unclear how he died. He said there was nothing at this stage to suggest his death was suspicious.
The body was removed from the river early this afternoon.
Police are trying to establish who the man is after he was found without any identification on him.
Mr Harvey described the man as caucasian, solid build, grey tidy hair, clean shaven, with "big, bushy eyebrows''.
He was found wearing a red and gold cycle helmet and a brown checked shirt.
Speaking on the banks of the river in the Woolston suburb of Christchurch, near where the body was found, Detective Senior Sergeant Harvey said: "We're really trying to identify just who he could be with the limited information we have.
"We found a relatively new mountain bike, which was left just up here (on the grassy river bank) and we wonder if it was associated with him because he had a cycle helmet on.''
The detective said their description fitted that of a man seen walking along Rutherford Street in a dazed state around 10pm last night.
He appealed for anyone who saw the man fitting the description to come forward.
