The Bradda Fell Race on Sunday has been postponed due to the snow.
The organising Manx Fell Runners inspected the course yesterday and found large parts of the route are still covered by drifts.
The Round Table Road is described as being completely blocked with snow as high as the hedge tops for large sections.
Marshal points are also inaccessible so the safety of competitors was a factor.
With cold weather set to continue into the weekend, an early decision has been made to postpone the race until the 16th June.
In order to give people a run, a race over the pier to pier course from Port St. Mary to Port Erin will run instead.
Entry will be £5 and monies will be donated to the Agricultural Benevolent Fund.