Great Swim have been forced to cancel this year's edition of the Great East Swim due to the presence of blue-green algae.
Due to be held at Alton Water in Suffolk on 25 September, the event had already been postponed once this summer back in June due to blue-green algae, however the situation has still not improved.
Great Swim said: "Recent tests have shown that water quality remains too poor for the event to take place.
"We have therefore been left with no alternative but to cancel this year's event.
"We're sorry that we have had to do this, but we hope everyone understands our priority has to be ensuring the safety of our swimmers at the event."
All entries will automatically roll over to next year's event, which will be held on 18 June 2022.