Jersey's Swimarathon is without a main sponsor for the first time in more than a decade.
Organisers are hoping local businesses will come forward to sponsor laps on each one of the five days of next month's charity fundraiser.
The Lions Club is offering firms sponsorship from 50p per lap, up to a total of £2,500.
Around 4,000 islanders of all ages are due to take part.
RBC's deal with the Swimarathon has ended after 12 years.
Brighter Futures, Caring Cooks, the Jersey Centre for Separated Families, Mind Jersey and Silkworth Lodge will benefit from the money raised.