Socialite Amber Nuttall has set out on her paddle board in an attempt to travel the length of the River Thames to raise money for charity.
The entrepreneur and environmentalist will make the 236 mile journey from source to sea for the Blue Marine Foundation on a stand-up paddle board, which looks like a conventional surfboard with a paddle.
A support boat is accompany her from Putney onwards to help her negotiate the tides, Thames Clippers, and other potential hazards.
Having undergone a rigorous training programme, the daughter of Sir Nicholas Nuttall - founder of the Bahamas Reef Environmental Educational Foundation, hopes to complete the sponsored challenge in a matter of days.
Ms Nuttall said: "I am excited to take on this challenge for a cause that means a lot to me personally having spent a large part of my childhood on, in and under the sea. Blue doesn't just talk about change, it makes things happen and I'm so proud to be an ambassador for them.
"I will be keeping my fingers crossed for fair winds and calm waters."
Charles Clover, from the Blue Marine Foundation, said: "Over the years, people have waded in mud, swum in icy waters and been photographed naked with fish for us. Paddling the Thames might easily be the most challenging yet.
"We are immensely grateful to Amber and hope she keeps her balance and that the floods hold off."
The charity aims to be able to secure the protection of 10% of the world's oceans by 2020 through a network of marine reserves and partnership solutions in the sea.