The Great North Swim in Cumbria has been postponed due to strong winds and heavy rain.
Around 900 people were set to take part in the two-mile swim on Friday.
This event has now been moved to Sunday, weather permitting, organisers said.
A one-mile event due to take place today has also been cancelled.
A statement on the event website said the decision was taken by the independent event planning group, as the weather forecast for today predicts strong gusting winds.
"Strong winds affect the ability of the safety kayakers to operate and also may make swimming conditions extremely challenging," the statement reads.
"The programme of events will continue as planned on the Sunday with weather conditions being monitored on a regular basis."
All participants will be offered a full refund of their event entry.
David Hart, of organisers Nova International, said: "We are sorry to cancel the one-mile event and fully understand the inconvenience this will cause, but the safety and well-being of our participants will always be our overriding priority."
All participants have been notified by email and text or phone message of the change.
The weather has also led to the cancellation of horse trials at Hutton-in-the-Forest, near Penrith.
Cumbria Police advised residents and visitors to take care and not attempt to drive through floodwaters, and walkers planning to visit the Lake District fells were also warned to make sure they are properly equipped.