The sheriff's office says they got a call a little after 5pm reporting spotting a body in the water about 2 miles from the dam.
Investigators say it appears the man had been submerged for an extended period of time. There were no obvious signs of foul play.
Crews have been searching for a missing swimmer in the area for over a week. But the sheriff's office is not confirming that this body belongs to that swimmer.
The Ada County Coroner's Office is expected to identify the man on Monday.