The lifeboat crew pulled up close to the rocks as the teen struggled furiously to keep himself afloat in the swell off Portstewart Head at 2.42pm on 25 September.
Seeing the danger that the swimmer was in, the brave lifeguard plunged into the sea to stop the boy drowning or getting hit by the rocks, and the pair were then reeled in safely by the rest of the crew.
The crew, acting under Coxswain Des Austin, were working amidst horrendous conditions including a force 6/7 north to northwest wind, and swells of up to two or three metres.
Utilising the good visibility, they pulled the boat alongside the rocks and spotted the teenager floating in his wetsuit and waving his arms, clearly in peril.
The tide was ebbing out, so there was a decent chance that the youngster could also have been dragged out to sea, especially if he'd been hit by the rocks.
The Coxswain expertly managed to draw the lifeboat as close to the rocks as could be safely achieved, whilst the mechanic from the lifeboat station rushed to put on some personal protective equipment and a dry-suit.
Once that was done, the mechanic went overboard, with only a line attached to the lifeboat to keep him safe.
After getting into the cold water, he managed to get across to the struggling swimmer and pull him to safety.
However, their ordeal was not yet over.
The boat then had to be manoeuvred around to position near the rocks, while the crew worked hard to drag them around to the starboard side of it.
Eventually, they managed to get the pair of them safely aboard the craft.
Once the casualty was on the craft, the crew that remained performed emergency care for the teenager, who was showing signs of hypothermia and exhaustion, as well as shock.
He was taken back to Portrush Harbour where his care was transferred to the Coleraine Coastguard and the Northern Ireland Ambulance Service.
Speaking afterwards, Coxswain Austin said: "Conditions were challenging at sea today and time was of the essence.
"The tide was turning at the time [the teenager] got into difficulty and the conditions were pulling him out to sea.
"The prompt actions of the lifeboat crew saved a life and we would like to wish [the teenager] well following his ordeal."
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