"A huge number of hours of work had already gone into it."
Any current plan for running the event under alert level 2 could be outdated by the time December 11 rolled around, Conder said.
"We are supportive around the [council's] decision-making, because at the end of the day, our event doesn't want to be the one that brings Covid to town."
He said 3 Bridges was one of the few marathons in New Zealand organised solely by volunteers, and this year's event had been tracking towards 1200 entrants.
Refunds would be available, minus a 10 per cent administration fee.
Registrations can also be transferred to 2022.
Whanganui District Council risk manager Debbie Watson said due to the current alert level requirements as guided by the Ministry of Health and Sport NZ, they couldn't approve the event.
"The activity of community sport is considered a social gathering and is limited to 100 people attending, while taking into account all the required public health measures and controls.
"The organiser of this event made an application for the use of a public space where the number of attendees would have exceeded the alert level limits."
There was a little bit of good news, however.
Conder said the Whanganui Harrier Club was hoping to offer a virtual race in early December instead.
Spot prizes and finisher medals would be sent via post.
"If we can do that then we're still giving something back to the community and to the people who have put all that time into training," Conder said.
"The course will be available on our website for people to have a look at.
"It's still predominantly a run on the walkways, so as long as you are socially distancing and doing all the right things, it's perfect."
More information on the virtual run would be released via the 3 Bridges Marathon website and social media platforms soon, Conder said.
He said Whanganui Harrier Club was grateful for the support from local companies in recent years, who had in turn allowed it to be "a viable club for the benefit of the Whanganui community".
It was vital the council continued to support the event as well, Conder said.
"Every year it feels like we are reinventing the wheel, and it is difficult.
"If you look around the country, there have been so many events that just don't happen anymore, and that's purely because things haven't been made easy, they've been made harder and harder."
In terms of the marathon's future, Conder said he was already looking forward to 2022.
"We're hopeful this event can continue going from strength to strength.
"There's so much potential for it to get bigger. It could easily become the best marathon in the country."