Event director Victoria Murray-Orr said yesterday the event attracted 473 individual and teams athletes in January this year and 200 in 2008.
The growth can be attributed to the inclusion of a half-ironman distance triathlon and strong interest from overseas athletes, who comprise 20% of the combined race fields.
At least 170 individuals have entered the long distance race (3.8km swim, 180km cycle and 42km run) and 50% were from overseas, she said.
Challenge Wanaka increased its marketing in Australia over the last two years and this year marks the first appearance by Tasmanians.
The Launceston Triathlon Club is sending 11 athletes, plus supporters.
"There's been a massive increase in interest from Australia. It has pretty much quadrupled, which . . . really shows Challenge Wanaka is getting better known in this part of the world," Murray-Orr said.
The professional women's field is shaping up very strongly, for the first time in the race's four year history.
Lisbeth Kristensen, of Denmark, is likely to take a race to Gina Crawford, who was last year's champion in a course record of 9hr 28min.
Kristensen has won several Ironman titles after rocketing into the spotlight in 2000, when she produced a startling debut Ironman time of 9hr 8min.
Other entrants are Irene Kinnegim, of The Netherlands, and Jodie Scott and Rebecca Preston, of Australia, all strong performers.
Simone Maier, of Wanaka, will make her debut as a professional athlete.
Wanaka's Merryn Johnston, who was second last January, has chosen to race this time in a team with Andrew McLeod, also of Wanaka.
The professional men's field is strong, with Chris McDonald, of Australia, returning to defend his title, which he won in January in a record time of 8hr 37min.
Richard Ussher has not yet raced Challenge Wanaka, withdrawing last January because he was ill.
He was third at Challenge Roth, in Germany in July this year, in 8hr 2min.
Keegan Williams, of New Zealand, second last January, is returning, as is third-placed Petr Vabrousek, of the Czech Republic.
Justin Daerr, of the United States, and 2008 champion Marc Pschebizin, of Germany, are also returning.
Brian Fuller, of Australia, described by some as an "uber-cyclist" among Ironman athletes, has also entered.
The 2007 men's champion, Luke Dragstra of Canada, who has raced three times in Wanaka, has decided not to return this time.
• The Challenge Wanaka Sports Trust announced yesterday it had chosen the Wanaka Rotary Club's schools reading programme as its main benefactor of the event's volunteer programme.
The trust will also support Mt Aspiring College's Spanish language group, which is raising funds to visit South America next year.
Challenge Wanaka has secured 200 volunteers but still needs 400 more people to help with the festival.
• The Central Lakes Trust has donated $13,300 to Challenge Wanaka for 50 cycle racks, a finish gantry and high visibility vests for officials, which organisers will make available to other event organisers in the region.
