All three emergency services were called to the banks of the Severn at Longney in Gloucestershire on Monday after reports a body had been found.
The police helicopter and the coastguard from Swansea helped recover the body from mud flats.
The fully-clothed body of a man was found about 50m from the riverbank.
Police are trying to work out the identity of the man, aged about 40, who is described as white, about 5ft 8ins, with straight, greying or mousey hair.
The coroner has been informed.