SHAWNEE, Kan. -- A man was found dead in a Johnson County lake on Sunday.

Park officials said the 31-year-old man was fishing in Shawnee Mission Park. He was found faced down in the lake.

Park patrons who found the man pulled him out and performed CPR. One of them was an emergency room nurse.

They were not able to revive him.

Park police Sgt. Chris Pennington said, "One of his poles was snagged. One of the possibilities is that he was going in to retrieve his snagged line, perhaps slipped on a slippery rock and fell, maybe hit his head. We can't rule out a heart attack. We won't know exactly what happened until the autopsy's done."

Ambulance personnel told KCTV5 News the man probably had a heart attack, because there were no visible cuts on his head.