Police divers are continuing to search a lake where a 13-year-old boy was last seen after being spotted in distress in the water.
Frogmen from Nottinghamshire Police and shore-line search teams in dry-suits have been combing the extensive Westport Lake in Stoke-on-Trent, Staffordshire, for a second day, after the alarm was first raised at 5pm on Monday.
Staffordshire Police said the underwater search was taking place in "extremely difficult conditions" at one end of the lake, where a witness last spotted the boy.
Efforts to locate the youngster started immediately following a 999 call on Monday evening, after three young males got into difficulties after going into the lake, officers said.
Two of the youngsters managed to get out the water before emergency services arrived, but the third child - who is from the local area - is still missing.
Chief Inspector John Owen, of Staffordshire Police, said a "systematic" search of the lake was now taking place.
He added that the boys' families were all "very upset and distressed" and were receiving support, while the emergency services operation is continuing.
The officer said: "We received a call just before 5pm at three young males in distress in the water.
"Two have made it out - we're still looking for a third at this time."
He added: "At this moment, speaking about the young male we're looking for, (he) is 13 years old, from the local area."
The other two youngsters are "of a similar age" he added, and are getting specialist help following their ordeal.
Police received a 999 call from a witness who had spotted the youngsters at the north end of the lake, near where it is bordered by the path of the Trent and Mersey Canal.
Mr Owen said: "We received a call there were males in the lake, we've arrived, two of the young males were already out - one male wasn't out.
"Clearly, we need to pull somebody out safe and well.
"We're on the following day (now), we've got specialist search teams here now searching the area, and searching the lake."
The lake's size and underwater conditions have presented difficulties in which to carry out the operation, the officer said.
"The divers are going to be working in murky conditions.
"Speaking to local fisherman here, it's extremely reedy and weedy at the bottom, they're working in extremely difficult conditions."
Mr Owen added: "It is an extremely large lake and I can't give timescales at all.
"We need to be thorough, we need to be systematic and we need to do things properly.
"In essence, sometimes it's a pace to make sure we don't miss things."
The officer said it was impossible to comprehend what the missing boy's family were going through, and they were being supported.
Group manager Brian Moss, of Staffordshire Fire and Rescue Service, said:" At approximately 5pm, yesterday afternoon, we were called to a report of three young people who were in distress in the water.
"Two of those young males did manage to get out of the water, and then an emergency call was made to report a third person was missing."
Emergency services have assembled an extensive team, including a specialist West Midlands Ambulance Service team and a Staffordshire fire brigade team, equipped with boats and waders.
A volunteer group, Staffordshire Search and Rescue Team, are also set to assist in what Mr Moss called a "methodical search".
He said: "It's an extremely difficult task because of the clarity of the water.
"Some places we've got shallow, clear water, but other areas we've got reed beds and the depth of the water increases, so the visibility diminishes.
"So that becomes a bit more difficult for searching.
"Depending on location, the search pattern is becoming broader and more difficult."
The lake is a legacy of coal mining associated with the area's historic potteries and industrial trade, though the fire brigade said it was the "clarity and size of the lake that's proving the difficulty".
Mr Moss urged people not to give into the "temptation" to go into rivers and open water during the hot days.
The body of water sits above the old Brownhills Colliery and was formed in 1884, when the workings hit the water table, flooding the tunnels and ground above.