Seven people aim to swim across six bays on Saturday - Castletown, Gansey, Port Erin, Peel, Laxey and Douglas.
And if that isn't hard enough, they will either cycle or run between the swims.
In total, each person will swim over 10 kilometres, cycle for 64 kms and run just under 17 kms.
The Challenge is being undertaken to raise money for the Isle of Man Commonwealth Games Association.
The Chairman of the Appeals Committee Martin Malone is one of those taking part - he's grateful the sea is relatively warm at this time of year:-
The Six Bay Challenge starts from the Sea Terminal at seven o'clock Saturday morning with the first swim across Castletown Bay at 7.45am.