Police divers recovered the body of a man from Lough Erne in County Fermanagh in the early hours of Monday morning.
The recovery followed reports that a 19-year-old had gone missing while swimming with friends near Castlearchdale Caravan Park.
It is understood he was last seen on Sunday afternoon. The body was found at about 0030 BST on Monday.
Sam McCreary from the Enniskillen lifeboat centre said lakes can be as dangerous as the open sea.
"It was beautiful weather yesterday and of course, it's the natural thing to want to go and get into the water but unfortunately water can be dangerous and this accident happened."