Children from Five Islands School will take part in their own ÖTILLÖ Swimrun this afternoon ahead of the main event this weekend.
J:ÖTILLÖ is a junior version of the endurance race - which features swimming and running in nature - giving young people the chance to experience the sport.
The junior event comprises four different courses for different ages.
Pre-school and key stage 1 group courses will only be go in the water up to waist depth, while Key Stages 2 and 3 have the option to go no deeper than their knees or take part in the full swim version by swimming in shoulder deep water.
Organiser Wez Swain described J:ÖTILLÖ as 'world first' activity for young people, saying: "This is a real community event and we welcome all children to take part and many more people to cheer on and help out."
He posted his most recent update on Facebook last night, writing: "We now have 151 people signed up!!!! The bags of bibs are packed and ready for distribution! We have plenty of bibs left for any late entries. See you all tomorrow for a great day!"
The four courses - click on photos to enlarge.
The courses will be heavily marshalled, with water confident adult first aiders on all beaches.
All Five Islands pupils will either take part in J:ÖTILLÖ or watch. There will also be a contingent from Mount's Bay Academy.
The event is not for profit, but donations will be collected for the Isles of Scilly Wildlife Trust.
J:ÖTILLÖ starts at Holgate's Green on St Mary's at 2pm.
The main ÖTILLÖ World Championships qualifying race takes place on Sunday, with the shorter Sprint version on Saturday.