An investigation was launched after the man's body was seen in the tidal River Ouse on Saturday, March 4.
Officers have been viewing CCTV footage of King's Lynn waterfront in a bid to find out what happened to the man.
Today a Norfolk police spokesman said: 'The body in the river was that of a 40-year-old Polish man from Lynn who was reported missing to us the following day. We had previously thought this was a missing person from Cambridgeshire, but enquiries ruled that out.
'The deceased's friend contacted police on March 5 to report them missing and subsequent enquiries established this was the man found in the river. The death is not being treated as suspicious and the matter will be passed to the coroner in due course.'
Firefighters had to be called in to help recover the body from the fast-flowing river. They donned waders and used a raft to bring the man ashore.
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