Police are investigating what may have caused a man's body to end up in Waikato River earlier this month.

The body of 38-year-old Phillip Mark Morris was recovered from the Waikato River on Thursday September 3.

Detective Senior Sergeant Ross Patterson said initial inquiries, including the results of a post mortem examination, led police to believe there were no suspicious circumstances in relation to Mr Morris' death.

"However we said at the time the investigation would continue into how he came to be in the river."

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Mr Patterson said the circumstances surrounding Mr Morris' going into the Waikato River remain 'unexplained'.

"Therefore we have engaged the services of the Police Special Search Group who will be searching the river's edge today while detectives conduct routine inquiries."

He said police were in the formative stages of the inquiry and asked anyone with any information to contact them at the Hamilton Police Station on 07 858 6200.