The Swimarathon has been cancelled on medical advice.
The annual charity event was due to start today.
More than 3,500 islanders were expected to take to Les Quennevais pool over the next 5 days to swim laps, raising money for local charities.
The popular event has been pulled on the advice of the Deputy Medical Officer of Health.
Doctor Ivan Muscat says the decision has been taken because of the spread of coronavirus across the UK and Europe - and the first confirmed case in Jersey on Tuesday.
“We are not currently calling for the cancellation of all large public events or calling for Islanders to avoid swimming pools altogether. However, given the large attendance, and spectators, in a warm, humid atmosphere, we are taking this precaution to limit the spread of the virus.”
Dr Muscat says the cancellation is not directly related to the island's first coronavirus case, nor to the self-isolation of 21 JCG students and teachers who recently returned from Italy.
Swimarathon organisers, the Lion's Club, have expressed their disappointment, and asked that people due to take part and their supporters consider continuing to donate so that the charities do not lose out.
"Whilst we are hugely disappointed by this, we would hope that teams who have collected funds for the benefit of the chosen charities may still donate the money to the Lions so that the five local charities may still benefit."
It is cancelled rather than postponed because organisers say there is no way of knowing how long the impact of coronavirus will last.
"We will be meeting and considering all options as the situation develops. We just hope that we can support our chosen beneficiary charities!"
Brighter Futures, Brightly, the Jersey Youth Trust, Teenage Cancer Trust and YouMatter were each expecting to receive up to £10,000 each from the sponsorship.
The 2019 Swimarathon raised a total £110,000 for worthy causes and the event has collected £3.5m for 120 charities since 1972.
Les Quennevais Sports Centre and swimming pool remains open as normal.
Up to date information is available on the dedicated section on the Government website: www.gov.je/coronavirus