“Officers received a report of a missing man around 6.10pm on Sunday (July 18),” said a police spokesperson.
“After extensive searches, a body was recovered from the water on Monday afternoon (July 19),” they added.
Police said that while formal identification has yet to take place, officers believe the body to be that of the missing 49-year-old man.
The death is not being treated as suspicious and the coroner’s office has been informed, police said.
The large-scale search at Ardingly Reservoir started on Sunday with help from the National Police Air Service helicopter.
Police said they had received a report that a 49-year-old man had not been seen since going swimming with friends in the afternoon.
West Sussex Fire & Rescue Service said they were called by Sussex Police to help them search the reservoir and that the search was suspended on Sunday at about 10pm because of nightfall.
“Crews from Crawley and Turners Hill fire stations were in attendance as well as our Technical Rescue Unit,” said the WSFRS spokesperson.
The search continued on Monday.