The Wanaka event is scheduled for January 19 and the new Auckland event for January 20 - leaving athletes with the choice of one or other, but not both.
Challenge Wanaka Sports Trust chairman Tom Pryde said he was "disappointed" at the Ironman organisation's choice of dates.
However, he noted entries for the 2013 Wanaka event were "dramatically higher" than they were at this time last year and that was despite the new Auckland event having been signalled for some time.
Mr Pryde took "a lot of encouragement" from the good Wanaka entries.
He was not aware of the reasons why Ironman had chosen a date so close to the Wanaka event and also to the Mt Maunganui half ironman event on January 5.
"Why they would want to butcher one of their own events is beyond comprehension."
Mr Pryde pointed out in contrast to Challenge Wanaka being run by a charitable trust, Ironman was owned by "a large corporate organisation in America" and "they are a full-profit organisation.
"The Auckland event is purely about making money ... Challenge Wanaka is about running a community event for the benefit of the community."
In April, Challenge Wanaka released an independently audited report that said the event brought $6 million of direct economic benefits to the Wanaka region.
Mr Pryde acknowledged how crowded the calendar for events was.
"It's impossible to protect yourself from a clash.
"There will always be events that come up and compete and you just have to take them in your stride."
Challenge Wanaka's "signature event" consists of a 3.8km swim, 180km bike ride and a 42km marathon run but the biggest competitor numbers are in the event over half those distances.
The new Auckland Ironman event was the same as the "Wanaka Half".
Ironman's chief marketing officer for the Asia-Pacific region, Jane Patterson, said her organisation had asked the Auckland Council for a date in December or January.
No date in December was available and New Year's Eve and a sailing regatta ruled out two January dates.
Of the two weekends left, January 20 was chosen after consultation with affected businesses in central Auckland.
Ms Patterson accepted Ironman was a business, but pointed out Challenge was a "global brand" and she suggested it might also be considered a business.
Wanaka Challenge's website says the Wanaka race is one of 11 worldwide in the "global Challenge family".
Unlike the Wanaka and Mt Maunganui events, the new event was restricted to individuals and not open to teams.
"I would hope that by staging an event in the city, which takes the sport to the people, that we are actually growing the pie.
"We are going to introduce to people, who may not have participated in triathlon in the past, the sport of triathlon and in doing so, if we are growing the pie, everyone benefits down the track."
