Organisers have been delighted to see entries flooding in for the event, which will be based at Westgate Leisure Centre.

More than 300 adults and 140 youngsters threw their hats into the ring before last Friday's deadline for entries.

The adult triathlon will begin at 7am, with competitors facing a 600km swim followed by a 42km bike ride and ending with an impressive 10km sprint to the finish line.

The junior aquathlon, comprising swimming and running, will take place after the triathlon and includes distances suitable for children between eight and 16 years old.

Triathlon competitors begin with their swim at Westgate Leisure Centre, followed by abike ride on a challenging course through Lavant, up South Harting Hill and back through Compton and Funtington, before returning to the leisure centre for an out-and-back flat run along Centurions Way.

People unsure about completing the triathlon have been allowed to enter in teams, who complete a different section each.

For under-16s, the aquathon is divided into age categories, with distances dependent on age.

Both events are being organised by Westgate Leisure Centre and Chichester District Council's sport and leisure team.

Last year's triathlon attracted more 150 athletes, local and from farther afield, but organisers were always confident more would take part this year.

The event is being sponsored by Natures Way Foods, who backed the adult triathlon when it was first held last year and are delighted to be able to extend that support to the new junior event.

Sarah Baldock, head of marketing at Natures Way Foods, said: "The Chichester triathlon was a real success in 2007 and it looks set to be bigger and better this year.

"We're very proud to continue our sponsorship in 2008, and to extend our support to Chichester's first junior aquathlon.

"As a local company, we're committed to helping local groups and initiatives that make Chichester a vibrant place to live, and the triathlon and aquathlon do that."