Three people have been treated for shock after being rescued from the sea near Aberthaw Power Station in the Vale of Glamorgan.
Coastguards said a 26-year-old woman and men, aged 21 and 19, were thrown from their dinghy on Sunday evening.
People on the shore heard cries for help and an RAF helicopter from Chivenor was called along with the coastguard and the Penarth lifeboat.
They were in the water for about 30 minutes off Gilestone Beach.
Once ashore they were taken by ambulance to the University of Wales Hospital in Cardiff, where they were all treated for shock.
Penarth Atlantic 85 lifeboat was already out on exercise when the rescue began at about 2030 BST and reached the trio in less than 15 minutes.
"As we approached, we could see a blow-up dingy and two people frantically waving to us from the sea. One woman had left the dinghy and had swum to shore," said Graeme Jones, who was at the boat's helm.
"One of our crew members, Jim Mayer, jumped into the sea and between him and the other crew - Sarah Mayer and Dan Forbes - we managed to get the two remaining casualties into the lifeboat.
"We then took them as quickly as possible to shore where we handed them over to paramedics."
Mr Jones a paramedic, was able to quickly update his ambulance colleagues on shore.
"These two young men were lucky that we were able to rescue them so quickly, as when we got to them, they were already in the early stages of hypothermia," he said.
"They were dressed in swimming costumes and had no lifejackets at all.
"It's vital to be aware of the change in the tides in the Bristol Channel, which can be treacherous and unpredictable, even in the summer, and it's also important to make sure you have all the necessary safety equipment before setting off to sea," Mr Jones added.