A mother has died after being recovered from the sea where, it is understood, she was attempting to rescue two children.
The victim was seen struggling in the sea at Waxham, Norfolk, at about 17:30 BST on Sunday.
The woman, aged in her 30s and who was staying with her family at a nearby campsite, had waded into the water to help the children.
She was recovered from the sea but pronounced dead on arrival at hospital.
The two children, one of whom is believed to have been in a kayak, are thought to have been unharmed.
Tony Garbutt, of HM Coastguard, said: "When people try to intervene they sometimes think they are stronger at swimming than they are.
"Cold water shock will kill you and that's what's happening. You get fatigued very quickly and you get overcome and that's when people get into tragic circumstances."
Mark Skerrett, of the Sea Palling Independent Lifeboat, said: "You see someone shouting and you just go in. You don't think about the dangers.
"But there were dangers there with the high rolling waves coming in and obviously the person was not strong enough to get herself out of trouble."
The woman's death is being treated as unexplained but not suspicious by Norfolk Police.
Supt Jason Broome said: "Colleagues from Norfolk Coastguard and the East of England Ambulance Service assisted officers with the incident.
"While inquiries are continuing to establish the exact circumstances leading up to the woman's death, this is a tragic situation and our condolences are with her family."
The UK's coastguard recorded its highest number of call-outs in a single day for more than four years on Saturday. Its teams dealt with 340 incidents and rescued 146 people.
Saturday was the second day of a mini-heatwave for parts of the UK, with temperatures hitting 34.5C (94.1F).