Rescuers pulled the body of a man from the River Wear after being alerted by horrified members of the public.
Passers-by raised the alarm at around 11.30am on Saturday after making the grim discovery opposite The Shipwrights, in Castletown, Sunderland.
Officers from Northumbria Police alerted coastguard volunteers, who later recovered the body from the mud flats near to the water.
The body was then taken to South Hylton Slipway and was handed over to police and paramedics.
Last night detectives investigating the discovery said it was too early for the man to be identified but it was believed he was middle-aged.
Helmsman at Sunderland RNLI Paul Nicholson said: “We worked closely with the police officers at the scene to ensure that the correct procedures were followed to allow their investigation to take place once the body was taken ashore.”
The death is not being treated as suspicious and a report is being prepared for the coroner.
A Northumbria Police spokeswoman said: “At around 11.30am officers attended the scene near to Ferryboat Lane where the body of a man was recovered.
“He has not yet been identified. There is believed to be no third-party involvement and a report is being prepared for the coroner.”
A spokesman from Sunderland RNLI said: “Shortly before 11.30am Northumbria Police received a 999 emergency telephone call from a member of the public reporting the sighting of a person lying on mud-banks at the edge of the River Wear opposite The Shipwrights, Castletown, Sunderland.
“Northumbria Police immediately passed the information on to Coastguard Officers at Humber Coastguard who requested the launch of Sunderland RNLI’s D Class inshore lifeboat.”
The news comes just weeks after the body of missing Jason Fyles was pulled from the River Tyne.
The Newcastle University undergraduate vanished after a night out in the city last month. Police recovered a body from the Tyne on June 26.