The elite men's road race route has been cut by 19km as weather conditions in the Yorkshire Dales would put the safety of riders and spectators 'at risk'.
The race will now miss some of Yorkshire's iconic climbs ,as it will not pass through Bainbridge, Hawes, Buttertubs, Muker, Gunnerside, Reeth, and Grinton Moor.
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Continuing heavy rain prompted the decision by race organisers UCI, the environment agency and local mountain rescue teams.
The route will divert at Bishopdale Beck just outside Aysgarth, and to direct riders east up Temple Bank and along the A684 to Leyburn where the race will continue as normal.
A spokesman said: "We know this will be hugely disappointing to the communities in these locations who have been planning events and celebrations to coincide with the race today. We are very sorry."
It comes after heavy rain led to two big crashes from the men's under-23 time trail at the Road World Championships in Harrogate.
Spectators who were hoping to see the race in Wensleydale and Swaledale should head to West Witton, Wensley or Leyburn where they can view the race as it passes through just before 11am.
There will also be nine laps of the Harrogate circuit before the finish on Parliament Street.
The men's elite race length is now 261km instead of 280km.
It is also setting of 20 minutes later than planned at 9am in Leeds city centre.