Two foiling kite surfers were rescued after getting into difficulty one mile off the Southend-on-Sea coast in Essex.
One of the surfers managed to call 999 and requested the HM Coastguard using his Apple Watch on Saturday.
The RNLI Southend Lifeboat and National Coastwatch Institution Southend (NCI) helped find the two kite surfers and bring them back to safety.
The surfers, who were thought to be at risk of hypothermia and secondary drowning, were treated at the scene.
At one point NCI observed the surfers had quickly passed the Shoeburyness Beacon and were potentially being swept past the Shoebury Boom in a "strong outgoing tide".
The NCI helped guide an RLNI lifeboat to the surfers, who were brought back to shore at West Beach.
There was concern that the casualties had been in the water for a considerable period and were showing signs of hypothermia and possible secondary drowning.
Paramedics from the Air Ambulance and East of England Ambulance Service observed the surfers and discharged them at the scene.
A HM Coastguard spokesman said: "Should you see anyone in trouble on or near the coast, don't hesitate to dial 999 and ask for the Coastguard, you could save someone's life."