About 300 people are expected in Cornwall in a bid to set a new world record for the biggest number of surfers riding the same wave.
They will be attempting the feat on Sunday at Polzeath beach as part of the Global Surf Challenge.
But they face tough competition with similar attempts taking place across the world.
The effort is part a project called Earthwave and organisers hope it will raise awareness about global warming.
Conrad Humphreys, a yachtsman who is taking part in the surf record attempt, explained how difficult it would be to get so many surfers in the water at once.
He said: "Luckily Polzeath is quite used to having so many people out in the water in one spot and there isn't a huge surf forecast for Sunday, so the waves should be quite small.
"But I think we'll need as many as possible because with these record attempts people end up missing the wave and not getting on it so if we start off with 300, we'll be lucky to end up with 100 by the end."
According to the organisers of the Polzeath attempt, the official world record stands at 44, set by Lahinch surf school in Ireland. However, unofficially the highest figure is 73, held by the Kahuna Surfing Academy in South Africa.