Competitors run on road and cross country
Organisers are worried that a race which pits man against train may be running out of steam after 26 years.
They say the 'Race the train' event in Gwynedd will end this year unless more volunteers come forward to help run it.
The 14 mile (22 km) race against the steam train at Talyllyn, between Tywyn and Abergynolwyn, attracts around 2,000 runners from all over the world.
It is run in August by local Rotary Club members and has raised more than £100,000 for charity over the years.
Race director George Watson said more volunteers were needed as there was just too much work involved.
Mr Watson - who has run the race for the past four years - said the work-load was a combination of administration, health and safety and the actual race itself.
"When the club began organising the race there were 25 or so members, but now there are only 14, and basically we need more bodies," he said.
Attracting members to the Rotary Club was a problem "everywhere" he said, and he would be quite happy if volunteers came forward just to help with the race.
"We want bodies with resources, people with 4x4s and a trailer to take things across farmland on the course.
"We need people who can shadow others so that there is someone there to take jobs over," he added.
Around 100 people beat the train each year
Despite the lack of support for organising the event Mr Watson said there was lots of support from the local community on the race day.
Around 100 of the runners taking part usually beat the train to the finish line.
Mr Watson, who takes a fortnight of his annual leave each year to run the event, said the final decision on the race future would be taken on 26 March after a public meeting at the White Hall Hotel in Tywyn at 1930 GMT.
This year's event will be held on Saturday 15 August.
Keith Lycett, Rotary added: "It is sad to see this day arrive.
"However, without more people being prepared to support the 14 members of Tywyn Rotary Club who have carried the event all these years, we just can't see how we can do this anymore.
"If anyone in the community is prepared to make a commitment to lend a hand by joining Rotary, we would reconsider, but without help it just has to finish," he added.