Swim Ulster has cancelled the Big Bay swim due to onshore winds and the swell that is forecast for Saturday 11th September 2021.
A spokesperson said "This decision has not been taken lightly and we have sought advice from the officials.
"We apologise for this, but such is the weather in Northern Ireland, that open water events cannot be guaranteed to go ahead.
"Above all else, the safety of everyone is paramount. We are working hard to try and rearrange this for Sunday 19th September 2021 and will keep you informed as soon as we know if this is possible. We are extremely disappointed as we have been looking forward to hosting an event in the North Coast, and in particular the spectacular beach in Portrush.