The bodies of three youths have been recovered from Ullswater in the Lake District, police said.
A search of Ullswater was carried out by divers
The three, aged 15, 17 and 21, and all from Wolverhampton, had been among a group enjoying a swim when one got into difficulty.
Another 15-year-old boy was pulled to safety in the incident, which happened on Saturday afternoon.
On Sunday afternoon, police named them as Harvinder Singh, 15, Tajinder Singh, 21, and Satvir Singh, 17.
Cumbria Police said the three victims were not closely related, but may have been from the same extended family.
The group had been staying in Glenridding, a village overlooking Ullswater.
Insp Sean Murphy, from Cumbria Police, said: "I think the lake was reasonably calm.
"Unfortunately it does have deep areas and shelving and the water is extremely cold so it's all speculation at the moment but I am assuming that someone has gone too deep and they have got cold and been unable to swim."
Members of the public and a lake warden went to help when the alarm was raised, and managed to rescue the 15-year-old boy.
He was taken to hospital, where his injuries were not thought to be life-threatening.
Boat worker, Zak Ratcliffe, said he had hired boats out to the group earlier and told how he helped to try and rescue those in difficulty.
"I got in a boat and went around and I couldn't see them so I jumped into the water," he said.
"It was a heat of the moment thing, I didn't really think about it, and I've been told it was the wrong thing for me to do as it put me in danger.
"There was a guy about to hire a boat off us and he jumped in as well but we couldn't see them anywhere. They were just gone, there was nothing we could do."
Searches by the coastguard, a helicopter and police and civilian divers were carried out overnight.