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He believes thieves must have stolen the safe and dumped it in the lake, possibly intending to retrieve it later.
Another magnet that he also found at the bottom of the lake – Pittville lake in Cheltenham – suggests the thieves had tried to find the safe but failed.
Adam, 22, had paid £17.50 for the fishing magnet on the internet to get him out of the house and try to make some money.
He said: “I cast it in about four or five times without any luck.
