An anonymous donor has pledged to give £300,000 to the two charities receiving funds from Susan Taylor's cross-Channel swim.
A spokesman for Virgin Money Giving, which is collecting funds raised from her swim for Rainbows Hospice for Children and Young People and Diabetes UK, confirmed that one donor had donated £150,000 to both of the organisations.
The donations are being verified according to the site's usual procedure for large gifts, he said.
Taylor died on Sunday while attempting to swim the English Channel to raise funds for the two charities.
Taylor, a 34-year-old accountant from Leicestershire, had been an ambassador for Rainbows for the past two years.
A statement from the charity said it had been advised to expect a gift of £150,000 from an anonymous donor.
"Susan’s family are very touched by people’s thoughtfulness and kind sentiments," it said.
Geoff Ellis, chief executive of the hospice, said: "Susan was extremely passionate about Rainbows and in the past two years she has done so many wonderful things to support us.
"Nothing was ever too much trouble and she was totally dedicated to fundraising for the hospice. On behalf of Rainbows, I would like to thank everyone who has honoured Susan’s memory by making a donation. The generosity of those who knew Susan, and those who didn’t, is incredible and we are very moved by everyone’s kindness."
A spokeswoman for Diabetes UK said the charity was aware of the pledge, but did not want to comment until it had been confirmed.