No further Great East Swim events will be held in Suffolk in the future due to the presence of dangerous algae at Alton Water.
Organisers of the swim, which regularly attracted thousands of people every summer, have confirmed the 2022 event scheduled to take place in June will not be held as planned.
The water in the reservoir near Holbrook contains blue-green algae, which can be harmful to humans.
Aqua Park Suffolk, which was previously hosted at Alton Water, was closed permanently in 2019 due to the algae.
A statement posted on the Great East Swim website said: "It is with sadness that we announce the Great East Swim will not take place in 2022 or in the future.
"The ambition was to bring a high quality open water swim event to Suffolk and we’ve thoroughly enjoyed seeing thousands of swimmers achieve their goals and raise significant funds for good causes.
"Unfortunately, the Great East Swim is not currently feasible in its current site in Alton Water, due to ongoing challenges with blue-green algae which has caused the event to be impossible to stage in 2021.
"We have explored ways to mitigate this as well as looking for other locations, but unfortunately, we haven’t found a solution to the problem, and we can’t continue to operate without confidence the event will go ahead.
"We would like to say a heartfelt thank you to Suffolk County Council and Anglian Water for their excellent support, and of course, to everyone who has taken part or supported the event."
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