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.

Princess Anne opens Jersey Zoo gorilla enclosure
Tarifa Jet and Caesarea Trader return to service
Jersey Post returns to profit
Could harnessing the youth vote change the election?
Inclusive island-wide fundraising challenge asks for 'moment of understanding'
Jersey ranks second in list of short-break destinations
HMS Tyne visits for Jersey Boat Show
Penalty shootout ends Jersey Bulls' promotion hopes