Busselton's premier event, the Sunsmart Ironman WA and Ironman 70.3 has been cancelled for 2020.
The Ironman 70.3 event that is cancelled is the one that is run alongside the full Ironman competition which was due to be held in December.
Triathlon WA's 70.3 event which was postponed in May, will be held on October 17 with registrations open until October 5.
The Ironman website stated that the organisation remained optimistic that the COVID-19 situation would have improved by the time the event was supposed to take place in December but the ongoing uncertainty was too high.
With the WA and international border restrictions still in place, the organisation could not keep trying to plan for the event which draws thousands of competitors.
City of Busselton Mayor Grant Henley said the local economy would be forgoing millions of dollars as a result of the event not proceeding this year.
"The Ironman 70.3 Busselton event is still proceeding so the loss will be somewhat offset by this fact," he said.
"It is, however, a tough blow for businesses already feeling the financial impact as a result of Covid-19 closures"
The Ironman website stated that the news would bring about mixed emotions for everyone involved in the event.
"Please know that our team is gutted," the website stated.
"We really wanted to end the year on a positive and see you back doing what you love."
All currently registered athletes have been sent an email from Ironman with details on their options, but if you haven't received this first email, please contact email@example.com.
"While we are prevented from holding the event in 2020, we are already looking forward to all of us coming back stronger in 2021," the Ironman website stated.
"Our team would like to thank you for your patience and support of the event and look forward to seeing you on the start line next year."
Mayor Henley said it was disappointing to see the event be cancelled.
"The event organisers are based in the Eastern States and at least 50 per cent of registered participants are from the Eastern States or overseas," he said.
"Given the uncertainty around border closures, the organisers had to make a call on the event proceeding now.
"It's a sad year for Ironman with many events across the world cancelled in response to the pandemic.
"However, the organisers have given the city a firm commitment to hold the event in Busselton next year and a date has been set - Sunday 5 December 2021."