"However, like any river there are significant flow variations and at times of higher flow things can get a lot different and that was the case yesterday."
The council was considering what actions to take to prevent further tragedies.
"We've got a problem with warning signs because when we put them up they get vandalised because it's a highly-trafficked area and a very popular recreational site, so we're thinking about whether we need to put up more robust signage that will withstand the rigours of vandalism.
"We can't stop people from swimming in rivers. What we need to do is just to show them the risk of rivers in higher flow because they're a much more dangerous beast than when they're flowing normally."
There was already a warning sign about 100 metres from where the young woman drowned, he said.
Council engineers were looking at whether there needed to be structural alterations to the waterway to make it safer.
"We've also got to remember that this is an important economic waterway for wider Canterbury and we've got to make sure that we don't limit our ability to service the farmers who rely heavily on this water source, but obviously we don't want to contemplate ever having another tragedy of a similar nature.
"We are just so gutted for the loss of a young life and we extend our condolences to the friends and family of this young person, it's just devastating."
Police could not be reached for comment.
