The discovery was made under the Leeds and Liverpool Canal bridge at Cowling Brow earlier this morning.
The area around the road bridge was sealed off as investigations continued.
Several police vehicles and an ambulance attended the incident.
A resident of Bridge Mill Court, adjacent to the canal, said she saw the police activity.
The woman, who did not want to be named, said: “As I walked down the canal I saw the police were on the opposite side of the road.
“I looked down the canal. It looked like a body under the bridge. I presume it’s a body.
“It looked like it had come out of the canal because it was all wet on one side.”
Joseph Kelly, 28, an employee of nearby Kerax, Cowling Road, said: “I’ve not seen anything.
“There were five police cars and an ambulance parked down there.”
Another worker said: “I walked down the canal about 7.15am. It hadn’t been sealed off then.”
A police spokesperson said: “We were called shortly before 6.30 this morning after reports that a body had been found under the bridge next to the canal at Cowling Brow, Chorley.
“The body is that of a man.
“Officers are still at the scene and enquiries are continuing to establish the identity of the man.
“We can’t say any more at this stage.
“It is still early days.”