Tomorrow's Great East Swim, at Alton Water Country Park near Ipswich, has been postponed and will not take place this weekend.
The decision was taken this morning as the weather forecast for the weekend predicts rain showers and strong gusting winds over Saturday and Sunday.
Organisers said strong winds affect the ability of the safety kayakers to operate and also may make swimming conditions extremely challenging.
Details of how to claim a refund will be communicated to entrants next week.
The swim website said: "We're extremely sorry to postpone the event and fully understand the inconvenience this will cause, but your safety and well-being is always our number one priority."
The Great East Swim was officially launched this morning in Suffolk.
The event in June will see thousands of swimmers take the plunge at Alton Water Reservoir near Ipswich.
Swimmers can chose from a half mile, to 5km swim, with thousands of pounds raised for charity at the same time.
Details have been announced of this year's Great East Swim.
The event at Alton Water near Ipswich, will take place on Saturday the 22nd June. The swim is now in its fifth year and offers five different courses ranging from half a mile to five kilometers.