Officials responded to a call about an unresponsive man who was pulled from the water at Marquette Park Beach just after 6:15 p.m.
A witness reported seeing the man, identified as 57-year-old Joseph Davis, alone and struggling in chest-deep water before he went under.
Two Good Samaritans pulled Davis out, but he was pronounced dead on the scene.
Officers on scene were told that a second person was missing in the water, but those reports were inaccurate, authorities said.
Indiana conservation officers are investigating, but foul play is not suspected.