The event made a significant loss last year and does not have any reserves to fall back on.
In 2016, when the race was at its peak, 1336 athletes lined up. Earlier this year, it attracted 567 athletes.
Challenge Wanaka Trust chairman Tony Pfeiffer said there was a real risk it would not go ahead next year.
"We are very, very nervous about it. We made a loss last year and now do not have any reserves. We need a positive outcome and if we do not get it then we will have to pull the pin," he said.
The trust has engaged an event specialist, Chris Randle, to help drive interest.
Mr Pfeiffer said the event had inbuilt costs, such as $70,000 for traffic management, which had to be paid.
Challenge Wanaka Trust event director Jane Sharman was more bullish about it going ahead next year.
However, unless more entries came in, the 2025 event would be the last, Ms Sharman said.
Changes had been made last year as the focus needed to switch back to the main Challenge half event.
There were still junior, intermediate and secondary school categories, which attracted nearly 2000 competitors, but the cross-triathlon and the Friday night short triathlon event had gone.
"The focus needs to go back on the Challenge half as that brings in the money to have these other events. You can’t have all these other events being subsidised by our main event."
There is an incentive in terms of getting entries in by Saturday, as the entry price increases next month.
There are 220 individual entries registered for the Challenge half but another 100 are needed. Eighty teams are registered but organisers have budgeted for 150 teams.
"We need enough entries to plan for the logistics of the event. We know people for some reason do not like to enter too early but we need them to enter now to deliver a world-class event.
"If we do not get the numbers then this will be the last one.
"We want to make it to 20 years."
Next year’s Challenge Wanaka, on February 15, would be the 19th.
Ms Sharman said all costs had gone up, as had the price to enter, but it was simply a reflection of costs increasing over the past year.
Cost might be a deterrent for some, she said.
"People are doing it tough. Instead of maybe doing three events a year they are just doing one. Multisport is an expensive sport."
She said half the income came from entries and the other half from sponsorship and benefactors. Organisers were looking for more benefactors to help.
The challenge would be based around the town centre next year, moving from Glendhu Bay. A comprehensive survey showed most wanted to take it back to the town centre.
Former Challenge Wanaka winner Dougal Allan said it would be a crying shame if it was canned.
"I stepped away from the Coast to Coast in 2014 and it [Challenge Wanaka] became my main event for a while. It helped me become a better athlete and raised my profile," he said.
"People come to Wanaka to swim in the lake, bike all the cool trails and run the tracks. Then they can bring it all together with this race.
"I know there is a lot of people planning to do it but have not entered yet. They need to enter to make sure it is around."
