Mendota officials said the victim and a friend were fishing from a boat in the manmade pond at about 10 a.m. when one of them stood up and fell over the side of the boat.
The other man ended up in the water but was able to make it to shore believing the friend was behind him.
Rescue units from Mendota and Oglesby were called to the scene around 12:30 p.m.
Wednesday afternoon, the man's body was pulled from the water. His identity has not been released.
The LaSalle County coroner and the Illinois Department of Conservation are investigating.