Partial human remains described as being in "advanced stages of decomposition" were found in the Columbia River near Woodland on Sunday night.
Cowlitz County deputies said the body appears to have been in the water for months or possibly even years.
Detectives said there are no obvious signs of foul play, but it is too early in the investigation to definitively identify a cause of death.
The person was wearing Levi 521 blue jeans with a slim tapered fit, size 29 waist and 32 inseam. There was also one size 8 Nike shoe.
The Cowlitz County Coroner's Office is working with Nike to determine the time the shoe was manufactured and sold and whether it is a man's or woman's shoe.
The coroner has been in contact with a forensic anthropologist in King County who will be assisting on the case.
The Cowlitz County Sheriff's Office is also working with other law enforcement agencies who have missing persons that may be related to this investigation.
Anyone with information about this case is asked to call Detective Sgt. Brad Thurman at 360-577-3092.
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