The man whose body was found near the Heathcote River has been identified as Jeff de Moulin, 41, of Christchurch.
Detective Senior Sergeant Brian Archer said police believe he was drinking with his female partner and another man near the jetty or steps at the end of Catherine St on Thursday evening.
Police are still looking to speak to this person and are asking him to come forward.
Detective Senior Sergeant Brian Archer said the body was found by a member of the public about 9am but it was likely the man had died overnight.
"At this stage the cause of death is unexplained and we are trying to ascertain exactly what has happened here," he said.
"The body is in a certain position and it is unclear why it is in that position; it could be natural or there could be some other reasons."
Up to 20 police officers are investigating the death and a crime scene examination of the site, alongside the Heathcote River in Catherine St, is under way to "rule out any foul play", he said.
Archer would not be drawn on details surrounding the position of the body or whether it had any injuries but he said it was "an unusual situation and in an unusual position and clearly we are treating this seriously".
A Woolston resident spotted the body this morning while walking her 11-year-old brother to school.
The woman, who did not want to be named, said her brother was checking the river for fish, as he did every day, when he called out that he could see a man lying face-down.
"I said, 'Oh, there are lots of drunk people who go there all the time'."
She called a friend to help her check on the man.
"She touched him and ... she said, 'Call the cops, he's cold'."
The woman said the man was lying in a "really weird" position and was dressed "casually".
Archer said police had a "reasonable understanding" of the identity of the deceased and it was likely he was a Woolston local.
A man who police believe was with the deceased last night has been interviewed and CCTV footage of the area would be analysed to work out their movements, he said.
An autopsy would be carried out on the body tomorrow afternoon to determine the cause of death, Archer said.
- The Press
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