The body of a yachtsman was found by a fishing boat in the English Channel early on Tuesday morning.
The man's body was recovered from the sea off Nab Tower, south of the Isle of Wight, and brought to Portsmouth.
"There [were] no reports of a 'Mayday' for a man overboard, and it is estimated the body [was] in the water no more than 48 hours," said police.
The identity of the man is not known but police said he was in his 30s and was wearing a Crewsaver lifejacket.
A post mortem examination will be carried out on Wednesday at the Haslar Hospital mortuary.