Brits are being warned to take care in and around open water after at least nine people died in incidents in the sea and in lakes during the Bank Holiday heatwave.Seven teenagers, a grandfather in his 60s and a woman in her 70s are known to have died - including two teenagers pulled from the water today.People have taken to local lakes and ponds in a bid to keep cool amid record-breaking temperatures, including the hottest ever daytime record of 35.1C that was set yesterday.But the Royal Life Saving Society has warned Britons to take extra care following a spate of water-related deaths, noting that 'warmer weather unfortunately sees an increase in accidental drownings'. And the emergency services are struggling to cope with increased demand - with London's ambulance service reporting its busiest day since the pandemic.Cheshire Police found a body in Pickmere Lake near Warrington earlier on Wednesday as they searched for a 17-year-old boy; Hampshire and Isle of Wight Constabulary said it had also recovered a body at Hawley Lake in Blackwater.On Bank Holiday Monday, 13-year-old Reco Puttock was pronounced dead after being found in Leadbeater Dam in Halifax, West Yorkshire; the body of a 16-year-old girl was found at Warwickshire's Kingsbury Water Park; and another boy was found at Rother Valley County Park in Rotherham.Fifteen-year-old Declan Sawyer died after getting into difficulty at Swanholme Lakes in Lincoln on Sunday; police in Lancashire recovered the body of a 12-year-old who got into difficulty swimming in the River Ribble.And heroic grandfather Phil Crow, 68, suffered a cardiac arrest as he ran out to the sea trying to rescue his wife and granddaughter after they got into difficulty at Tregirls Beach in Padstow, Cornwall on Monday.Phil Crow, 68, suffered a 'cardiac arrest in the sea' while bravely trying to help two relatives who got into difficulty in the water at Tregirls Beach Reco Puttock was rushed to hospital after being pulled from Leadbeater Dam in Halifax