Searches have been continuing for a third day to locate a 13-year-old boy who went missing at a lake.
Ryan Evans disappeared after getting into difficulties in Westport Lake in Stoke-on-Trent on Monday afternoon.
Two other youngsters, aged 12 and 13, managed to get out by themselves.
A joint emergency services search effort to find Ryan has been bolstered by sophisticated sonar equipment and sniffer dogs, Staffordshire Police said.
Police divers and specially trained water rescue fire and ambulance crews have also been deployed since the alarm was first raised at 5pm on Monday.
Chief Inspector John Owen said there was no estimate how long the searches may take, amid the "complexities" of the terrain, including the sheer size of the lake.
He said: "We appreciate we are now almost 48 hours into the search for 13-year-old Ryan Evans and we continue to do all that we can to locate him.
"Westport Lake is a hugely expansive area and at this time, we are unable to estimate how long the search might take.
"There are lots of complexities that arise during searches of this scale and we, together with our partners, continue to assess the resource and equipment utilised so we can cover the area as quickly and as thoroughly as possible.
"Conditions at the lake are such that we have shoulder-to-shoulder walking search teams in the water, divers and underwater search technology.
"We also have teams continuing to search the surrounding perimeter of the lake."
He added: "Our thoughts remain with Ryan's family during this extremely upsetting time."
Mr Owen also thanked a steady stream of well-wishers who have been passing on good wishes, and handing over ice lollies and cold drinks for the dozens of emergency service personnel working amid high temperatures.
Ryan is a pupil at Stoke's Haywood Academy.
A school spokeswoman said: "We are deeply shocked and saddened by the current situation.
"During this difficult period we have made sure that professional support is in place for students to access."