Organisers have announced the cancellation of this year's Festival of British Eventing at Gatcombe Park in Gloucestershire.
The high-profile event was due to start next Friday with British championship classes at open, intermediate and novice levels.
But it has now been called off due to the inclement weather and becomes the latest major eventing competition to fall by the wayside this season.
The Mitsubishi Motors Badminton Horse Trials and Chatsworth event were casualties in May, while numerous lower-key competitions nationwide have also been rained off.
Gatcombe co-organiser, Captain Mark Phillips, said in a statement: "The unprecedented rainfall over the last month has produced exceptionally wet ground conditions.
"Due to the continuing unsettled weather, we are unable to safely continue the preparations for the Festival.
"We know that riders and spectators will be disappointed - especially as so many events have been cancelled already this year.
"We did everything possible to ensure that the event took place, but sadly the hard-working ground crew at Gatcombe Park have been defeated by the weather."
British Eventing's chief executive Mike Etherington-Smith added: "The organising team has explored all options to see if there is a way to make the Festival happen, but it has simply not been possible.
"We will do all we can with regard to re-scheduling the British Championships later in the year and will keep members updated as, and when, we have plans in place."
One of Gatcombe's planned highlights this year was to have been a parade of Britain's Olympic eventing team - William Fox-Pitt, Mary King, Tina Cook, Zara Phillips and Nicola Wilson - next Sunday afternoon in the main arena in one of The Queen's State Range Rovers as a send-off just two weeks before London 2012.
Numerous top riders had entered the competition, including the British Olympic quintet, London-bound New Zealanders Andrew Nicholson and Mark Todd, plus Australian Olympic riders Clayton and Lucinda Fredericks.