Update 16.35pm: Police from the Major Crime Squad are investigating the discovery of a man's body in the Canning River this morning.
Police are treating the man's death as suspicious.
The body was found by children taking part in a kayaking lesson near Royal Street, Kenwick and reported to police about 8.40am.
A group of about 14 high school students saw the man's partly submerged body.
One of the kayakers said the group was shocked and traumatised by the discovery.
Water Police are among several police examining the scene.
The age of the deceased person has not yet been released by police.
A police spokeswoman said the cause of the death was unclear.
"We are unsure of the circumstances at the moment," she said.
Police have called for anyone who witnessed anything suspicious near the Canning River or Royal Street in Thornlie in the past 48 hours to contact CrimeStoppers on 1800 333 000.