The discovery was made under the Leeds-Liverpool Canal bridge at Cowling Brow in Chorley shortly before 6.30am today.
The man has been named locally as Kieran Dearden, who was in his 20s.
The area around the road bridge was sealed off this morning and an investigation launched.
A police spokesman said the death was not being treated as suspicious and a file will be passed to the coroner.
Tributes have been paid to Kieran on Facebook.
Leon Kemp said: “Rip bro gunna be missed x”
Laura Leadbetter said: “R.I.P Kieran xxx”
Kim Lucas said: “Poor soul. Rip”
Nicolla Moran said: “Oh no god bless x”
Liz Stobart said: “Rest in peace. Took to soon xxx”