Originally from Colney Heath, a former ironman contestant who once rowed across the Atlantic Ocean has set his sights on becoming the fastest man to ever run a marathon while dressed as a tree.

Isaac Kenyon will be taking on the Guinness World Record at this year's London Marathon - taking place on Sunday (April 21) - to raise awareness about the climate crisis.

The 30-year-old will also be celebrating Earth Day, which falls on Monday, April 22.

Isaac is hoping to complete his challenge in around four hours, despite wearing the cumbersome tree costume, weighing in at seven kilograms.

Herts Advertiser: Isaac and his costumer for the marathon.Isaac and his costumer for the marathon. (Image: Supplied)

The current world record for completing a marathon while dressed as a tree sits at four hours, five minutes and six seconds.

Isaac said: "The outdoors has helped me in my anxiety battles over the years.

"Nature has always been my answer. It has been my entire life.

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"It is important to me to protect nature on a personal level, for my own wellbeing, but also for Earth's eco-systems, which we are a part of.

"Without good access to nature I'm not sure how my mental health and anxiety would cope, it's my lifeline and is vital for everyone else too.

Herts Advertiser: Isaac will be raising awareness of the climate crisis during his run.Isaac will be raising awareness of the climate crisis during his run. (Image: Supplied)

"Taking on this challenge is a way of giving back to nature which has saved my life and of reminding people that every action, no matter how small, contributes to a cleaner, greener world, and a bright future."