Paul Gallihawk, 34, disappeared during the 750-metre open water swim at the start of a triathlon at Leybourne Lakes in Maidstone, Kent, on Saturday.
His body was found in the lake yesterday by search teams.
The advertising consultant had set up a Just Giving fundraising page to raise money for Kings College Hospital in South London which had cared for his father last year.
It had a target of £300 but today had reached more than 40 times the figure as wellwishers donated in his memory.
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