A 19-year-old fish farmer is believed to have fallen into the sea off Changi Beach last Friday and drowned.
The Myanmar national was brought to shore by passers-by at about 6pm the next day.
Fish farm owner Phillip Lim, who happened to be in the area, said he saw the man on a pontoon with three of his colleagues when he left his farm at about 10am on Friday.
When he returned, Mr Lim, 55, found out that the man, who worked at a neighbouring farm, had fallen into the water.
Mr Lim told The Straits Times: "I immediately got my diving gear and started to look for him. I spotted him, but the current was getting strong and I couldn't get to him. I ran out of oxygen."
He stopped his search at noon, after an hour. Mr Lim said that by the time professional divers arrived, it was about 3pm.
The Singapore Civil Defence Force said it received a call at 11.20am about a person missing in the waters off Pulau Ubin. It dispatched a marine fire vessel, which arrived at noon, and conducted a surface search in the area till about 4pm.
Mr Lim said: "I felt so helpless. This is somebody's child we are talking about."
He activated 10 fellow members of a volunteer search team called Sea Angels, and they searched for the man till 8pm on Saturday.
According to beachgoer Rohana M.D., a passer-by spotted the victim's body floating in the water on Saturday. Two other passers-by then pulled the body to shore. The police were alerted at about 6pm and the victim was pronounced dead by paramedics shortly after.
Jalelah Abu Baker