A man pulled unconscious from the sea died despite a frantic effort by sunbathers to save his life.
Lifeboat crews, coastguards and paramedics were at full stretch throughout the weekend as thousands flocked to the coast lured by the 27C temperatures.
A teenager cooling off in a canal drowned, two men were rescued when their dinghy drifted out to sea, a night swimmer was plucked from a fast-flowing river and ten children had to be brought back to safety after being washed away on inflatable beach toys.
Paramedics received more than 1,200 calls in 48 hours, many relating to the hot weather.
In Hove, swimmers pulled the man's body ashore to the beach off Third Avenue before giving him the kiss of life.
Paramedics raced to the front and took over the attempts to restart his heart but he was found to be dead when he reached hospital.
Police were today trying to trace relatives of the man who is believed to have been visiting from London.
Officers were called to the Royal Military Canal, near the Scots Float sluice gate, Rye, earlier on Saturday after an 18-year-old swimmer failed to resurface.
His distraught parents watched from the bank as two teams of divers searched in vain for their son. A police helicopter hovered overhead and paramedics waited nearby. His body was recovered several hours later.
Police said both deaths were being treated as tragic accidents and inquests would be held to establish exactly what had happened.
A Brighton lifeboat spokesman urged people to take extra care during the hot weather.
He said: "On hot days it is so tempting to take a dip but the sea temperature right now is only about 13C to 14C and that is cold."
Two men had to be rescued last night when they the dinghy they were paddling started drifting out to sea.
The men, in their early 20s, saw the boat floating off Brighton beach and decided to swim out and try and bring it ashore.
But the wind blew them further out to sea and they were just south of the Palace Pier when Brighton inshore lifeboat was launched at 8.45pm.
In Shoreham harbour, a man was saved from drowning after betting friends he could swim across the fast-flowing River Adur on Saturday night.
Lifeboat and coastguard rescuers reached him at 11pm as he clung to the footbridge.
Thirty-four children aged between three and 12 had to be helped by lifeboat and coastguard crews over the weekend at Camber Sands, near Rye. About ten had floated off on inflatable beach toys.
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