Dorset Police said the body was found in a river in the town of Christchurch at 1.04 pm on Monday.
In a statement, the force said it is believed to be that of missing Steve Grey (51) who travelled from Guernsey to Poole on a planned trip on 27 March.
He was last seen on Saturday 8 April.
The local coroner has been informed but formal identification has not yet taken place.
