Waikato Police investigating the homicide of John Isaac are appealing for sightings of the victim or unusual activity around the Waikato River.

Fifty-two-year-old John Isaac of Hamilton was located deceased in the Waikato River by members of the public on Thursday, January 18.

Police subsequently launched a homicide investigation following a post mortem examination.

To protect the investigation at this early stage, police are not in a position to elaborate further on the cause of death, says Detective Senior Sergeant Ross Patterson.

"Police are continuing to piece together Mr Isaac’s movements in the days and hours leading up to his death and are appealing to anyone who may have seen or interacted with Mr Isaac in the days prior to Thursday, January 18.

"Mr Isaac is believed to have been travelling around the Hamilton area where he resides and was last seen wearing black cargo pants and a green pattern camouflage t-shirt."

Ross says the investigation team would also like to hear from anyone who saw any unusual activity near the Waikato River at any of the bridges between Hamilton and Ngaruawahia on the afternoon of Thursday, January 18.

He says anyone who was out on the river or its pathways and banks and may have been recording recreational activities or taken photos or video on their phones is asked to please contact the inquiry team. 

Anyone with information is asked to call 105, or make a report online at 105.police.govt.nz, clicking “Update Report”.

Please reference the file number 240119/8775.

Information can also be provided anonymously to CrimeStoppers by calling 0800 555 111.

"This is an incredibly distressing time for Mr Isaac’s whanau who are being supported by NZ Police and Victim Support.

"The public can also expect to see an increased police presence along the Waikato River area while inquiries are conducted in the next few days."