The annual Bolton Ironman race has been shortened by 17 miles due to the ongoing fire at Winter Hill.
The cycling part of the race, which goes through Chorley and Leyland, has been cut from 112 miles to 95 miles, with the cycling route down the A675 and A674 being scrapped to ensure the safety of athletes, volunteers, marshals and staff.
A race spokesman said: “We tried everything we could but it came down to the police and the council.
“We understand the frustration, we know it’s not ideal.
“[But] it’s the only way to make it work without cancelling the whole race.”
Race organisers also calmed worries over air quality, adding that “no increase to normal readings” have been detected by environmental agency teams in the area.
Dave Russel, Assistant Chief Fire Officer at Lancashire Fire and Rescue Service, said: “The Ironman contest is something we have throughout wanted to see happen, but given the dynamic nature of the incident, it has not been possible to predict with any certainty that it could go ahead, or if it could, the extent to which our response and responsibility for competitor and general public safety might impose some route changes."
He added: "The public have responded magnificently throughout, co-operating willingly to our requests concerning access and fire and other appliance movements, in addition to their truly overwhelming messages of support and regard.”
A spokesman for Lancashire Police added: "We have worked closely with Lancashire Fire and Rescue Service, Lancashire County Council and the event organisers and agreed an amended route for the bike leg of this weekend’s Ironman event.
"These changes are first and foremost about public safety and the need to keep people away from the moors and to allow emergency responders to get on with their job.
"The fire service are still dealing with a major wildfire and need to maintain access to a large area in case there are any flare ups and this could be compromised by competitors and spectators.
"We are sorry for any disappointment the decision has caused but it has been done with public safety as a priority."
Some race goers have taken to social media to show their frustration with the decision.
In a tweet to race organisers, Jona Carrington said: "Can you confirm whether refunds/deferrals will be an option as the Bolton race is now not a full distance race? Possibly not even a triathlon?"
Adam Diver added: "The Bolton Ironman route isn’t the full distance. Wow! How is this possible at this stage.
"I fully understand the circumstances - I have friends putting out the fires - but it’s short of 17 miles."
On Facebook, Ian Hoffman, from Bristol, said: "I'm sorry Ironman but this is disgusting. You built your entire brand around the challenge of becoming an Ironman for which you plaster the distances all over the place.
"Then take away the opportunity to do that on six days notice. After 30 weeks of early weekend starts, battling through wind, rain, snow, hail, three beasts for the east, missed events, poor sleep, essentially structuring your life around the commitment to this challenge to have it taken away this close is crushing."
Each competitor paid a £400 entry fee to take part in the race this Sunday (July, 15).