It will be her longest challenge yet - which has also included running marathons previously - as the round-Manhattan Island swim is 28.5miles longer than the Channel swim.

It will take her past many iconic landmarks, including under all 20 of New York's bridges.

Pictured: Brooklyn Bridge is one of 20 Rosie will swim under. 

Rosie had to be selected to do the swim and is one of fewer than one hundred swimmers who are allowed to do the swim in 2019.

She will be the first Guernsey person to attempt the challenge and completing the swim will mean that she is two thirds of the way through the famous long-distance Swimming 'Triple Crown'. The third swim is from Los Angeles to Catalina.

Rosie is due to start swimming at 09:00 New York time on Saturday 17 August, which is 14:00 Guernsey time.

Her dad, Alun Williams said swim times are unpredictable but Rosie expects to take about eight hours.

Ahead of getting in the water, Rosie said; 

"I’m looking forward to the swim. It is an iconic experience and I’m just hoping that conditions will be favourable. It’s great to see so many Guernsey swimmers attempting long distance swims. Mine is just one of a number of swims taking place over the coming weeks. We all support each other so let’s hope it goes ok."

Rosie will be supported by a kayaker and a New York boat and her swim can be tracked here. 

Pictured top: Rosie Williams and her dad Alun.