Actor James Norton and Olympic swimming gold medallist Rebecca Adlington are set to take part in a 10-hour swim relay challenge on the Kent coast to raise funds for marine conservation.
They will plunge into the cold waters at Joss Bay, Broadstairs, at 07:00 BST on Friday.
All proceeds raised will go towards the Blue Marine Foundation, a charity dedicated to restoring the ocean to health by addressing overfishing.
Ms Adlington said: "I'm thrilled to take part in the Wild Blue Swim Challenge at such a stunning location as Joss Bay and to be joined by so many swimmers united for a cause that truly matters is amazing."
Mr Norton added: "Like everyone, I'm in awe of the ocean.
"It's wild, powerful, and under threat…this [challenge] is about protecting biodiversity and reconnecting with the natural world before it's too late."
According to research reported by Blue Marine Foundation in July 2024, there has been a 92% UK reduction in seagrass meadows and a 95% decline in native oyster reefs over the last century.
All proceeds from the swim will go towards funding vital projects focused on reviving of both these underwater ecosystems.
