An anonymous donor has pledged £300,000 to the charities Susan Taylor was fundraising for when she died swimming the English Channel.
The 34-year-old, from Barwell, Leicestershire, collapsed in the water just a mile off the French coast on Sunday.
About £3,000 had been raised by Monday but donations have since poured in.
The money will be split between Rainbows Hospice, in Loughborough, and Diabetes UK.
The total on Ms Taylor's fundraising website stands at about £70,000 but the charities have been contacted and told of the extra £300,000.
Rainbows said Ms Taylor would have taken heart from the donation.
Karen Payne, the charity's spokeswoman, said: "She always tried so hard to raise money and raise the profile of Rainbows and we really think she would take some comfort in knowing that her efforts weren't in vain.
"[The £300,000] is absolutely fantastic. When we heard about it we were very touched - not only with this donation but with all of the donations we've received," she added.
The hospice, which works with East Midlands' children and young people who have life-limiting or terminal conditions, has been in touch with Ms Taylor's family through her swimming coach Paul Ferrier.
They are said to be "touched by people's thoughtfulness and kind sentiments".
Earlier this week, the family released a statement saying she was an experienced long-distance swimmer.
Earlier this year Ms Taylor told BBC Radio Leicester it had been a childhood ambition to swim the Channel and she gave up her full time job to complete the challenge.
On Sunday evening she was airlifted to Boulogne by the French navy where she died in hospital.