Why don't we know more about cold water shock?

At least eight teenagers have died after getting into difficulty in open water during the UK’s record-breaking heatwave.The tragedies have caused the Royal National Lifeboat Institution (RNLI) to warn of the dangers of “cold water shock”, as many try to cool down in the baking heat.The deaths have also happened days before the official start of summer - so what can be done to keep people safe in the months ahead?Mhari Aurora discusses water safety with campaigner Beckie Ramsay, whose son drowned in open water in 2011.Have you got a question for This Is Why? Email the show – why@sky.uk.