A firm has been ordered to pay £100,000 after a 16-year-old boy in its care drowned on a trip to an old sand quarry.
Castle Homes Limited, which ran Castle Lodge home for young people, in Cambridgeshire, admitted breaching health and safety regulations over the incident in July 2013.
Two support workers also faced charges over the death of Umar Balogun, from Waltham Forest, north-east London, but were cleared following a trial at King's Lynn Crown Court.
At the Old Bailey, Judge Mark Dennis QC ordered Castle Homes to pay a fine of £80,000 and £20,000 prosecution costs to the Health and Safety Executive.
He said the death exposed "flaws in the system" as well as "obvious errors" on the day, including failing to make a risk assessment for the trip.
Both staff members who went on the trip were "raw recruits" when there was another more experienced person who could have gone, he said.
At an earlier hearing, prosecutor Quentin Hunt said the company had pleaded guilty in April last year.
Outlining the case, Mr Hunt said employees of the home had taken boys on a trip to Bawsey Pits (pictured) near King's Lynn on July 16 2013.
The staff made no efforts to stop Umar and another boy from getting into the water even though there were a number of "No swimming" signs.
Mr Hunt said: "Mr Balogun was seen to duck under the water and did not reappear.
"Mr Balogun may have got caught out by the changing depth. He subsequently became entangled in weeds and drowned.
"A diver was sent to the scene and subsequently recovered the body."
Castle Lodge offered one-to-one care of youngsters who "showed signs of sexually inappropriate behaviour", the court heard.
Mr Hunt, for the Health and Safety Executive, said that while there were "generic risk assessments", individual assessments were not made for trips like the one to the pits.
The lawyer said there was "systemic failure" at Castle Lodge which went on over a "long period".
He said: "The failings of the company amount to high culpability. The company was directly and immediately responsible for the trip from the home which resulted in the fatal accident."
He highlighted "inadequate" training and induction of staff and said ad hoc trips had no proper risk assessment.
Mitigating, Angus Withington said Castle Lodge was shut down "effectively as a moral decision" as it was thought to be "the right thing to do".
He outlined changes Castle Homes had made in the wake of the accident.
They included a requirement for temporary staff to read health and safety documentation, enforcement of "group leader responsibilities", and training in "dynamic risk assessment".
The barrister added that there was a system of discussing weekly activities well in advance which could not be changed without "written authority of the registered manager".
Judge Dennis told the court that the popular country park where Umar died had "hidden dangers" in the water, including steep drop-offs and weeds which would "quickly and perilously entangle" swimmers and divers.
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