Around 600 triathletes are expected to compete in this weekend's 10th annual Norwich Triathlon at Whitlingham Country Park.
The event was first held in 2005 with around 100 competitors but has expanded to become one of the eastern region's main triathlon events.
The sprint triathlon will be held from 6pm this evening, taking in a 750m open water swim in Whitlingham Great Broad, followed by an 18km cycle and a 5km run.
The Norwich Olympic Triathlon will then be held from 8am tomorrow, starting off with a 1.5km swim at Whitlingham, a 39km cycle and a 10km run.
The weekend, organised by Tri-Anglia triathlon club, will attract athletes from around the country, with the sprint triathlon also doubling as the Eastern Region Sprint Championships.
Tri-Anglia chairman Rob Lines said: 'There were about 150 or so in the first year and it's grown progressively since. We've changed the format slightly now though. We've always had an Olympic distance but we have moved the transition area now (from swim to cycle).
'In the first couple of years it was by the lake and we've moved it to by the flint barn at Whitlingham, so we could offer more people the opportunity and the uptake has steadily been growing up to this point, to having two separate races where we can have 500 in one race and 500 in the other.'
According to British Triathlon, the sport is now the fastest-growing in the UK, at a rate of around 10pc a year and particularly with people between the ages of 35 and 50, to around 110,000 active triathletes.
That increase follows the success of the Brownlee brothers, Alistair and Jonny who won gold and bronze respectively for Team GB during the London 2012 Olympics.
The eastern region also has a number of elite triathletes including Lowestoft professional Joe Skipper, current men's 35-39 world champion Matt Ellis and the British sprint and European Olympic distance champion in the same age category, Iain Robertson, both of whom are Tri-Anglia members.
With last year's winner Ellis a fitness doubt, Lines expects Robertson to be pushing for the win in the men's race and is also predicting a tough battle in the women's race.
Kim Morrison, from Bale, near Fakenham, joined Robertson in claiming an age group gold medal at the European Triathlon Championships in Kitzbühel, Austria, last month – claiming the women's 25-29 age group gold.
Lines expects Morrison and Essex triathlete Emma Stevens, who has been studying at the University of East Anglia in Norwich, to be fighting for the women's title.
'It's always daunting hosting a race but similarly exciting,' Lines added. 'It's like pre-race nerves for a competitor with all the organising headaches but we're just hoping that they all do well and get on well with the spectators and things like that.'
The event also includes a Business Challenge – a three-person team event, with a new format designed to attract even more people into the sport.
'This year we have changed the format of the Business Challenge because we want to encourage even more people into triathlon,' race director Mark Philo said.
'Instead of the previous relay event where team members did either the swim, the cycle or the run – this year everybody has to do all three.
'Many team members will try the whole event for the first time. We hope this will give them a taste for the sport and encourage them to enter other triathlon events as an individual.
'We've found that people often assume triathlon is too gruelling for them, but when they are encouraged to try the whole thing, they get a taste for it.'
For more information about the event, go to www.tri-anglia.co.uk
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