People taking part in the extreme sport of ice swimming have been told the water is not cold enough to break official records.
But the British Ice Swimming Championships are still going ahead at Sandford Parks Lido, Cheltenham, with competitors coming from all over the world.
Event director Kate Steels said: "Unfortunately the water is a little bit too warm for us."
The water must be colder than 5C.
Ms Steels said: "We count ice swimming at temperatures of 5C and below and the water is 6.4C, so it won't count in terms of our records but it will be recorded as the event and we've got event medals and everything like that.
"I think to be honest, anywhere's too warm. I know where they train, up in Hatfield in Yorkshire, where they do ice miles - the water's too warm.
"It's a sign of climate change - everywhere's too warm at the moment."
She said more than 60 swimmers were taking part and included people from Argentina, South Africa, Germany and France.
Cold-water swimming can be dangerous - with a significant risk of hypothermia when not done in a controlled setting.
Jonty Warneken, from the International Ice Swimming Association, said swimmers had to "be careful and take it steadily" due to "cold water shock".
He said: "We usually see the dramatic and sad effects in the summer, when kids jump into canals and quarries that are still at really quite low temperatures in comparison to the outside temperature.
"And basically you shock your heart and then what usually happens then is that you take a gulp of very cold water and things start to go wrong very quickly."