About 200 entries are expected for the race this weekend, half the usual number.
Co-ordinator Graeme Duncan said it was unfortunate Challenge Wanaka Triathlon Festival - a long-distance triathlon and other shorter-distance events - had been moved to the same weekend.
''It's the first time we have had a similar event on the same weekend in Central Otago. It's very annoying.''
Previously, Challenge Wanaka had been held in mid to late January.
The rail trail duathlon had been held on the last weekend of February since it began in 2000.
Mr Duncan said the rail trail duathlon, organised by Lions clubs on a volunteer basis, was stuck with the dates.
''We have looked at alternatives but they don't work. We run into other clashes with other events.''
Percentage-wise, the drop was the biggest faced by organisers in one year.
Entries peaked six years ago about 650, after steadily increasing since the race began, Mr Duncan said.
Half the money raised by the non-profit event was spent on developing the rail trail and the other half went to the Lions clubs who ran it.
''It's the community that misses out here.''
Competitors will line up at the start in Clyde tomorrow before tackling the 150km rail trail in alternating running and biking stages over two days, stopping in Ranfurly at the end of the first day and finishing in Middlemarch on Sunday.
