The victim, who was seen having difficulties in the rip current, was recovered from the water by lifeguards who performed CPR, Dorset Police said. An air ambulance and paramedics attended, but the man, believed to be in his 50s, was pronounced dead at the scene.
He is believed to have had a cardiac arrest, a spokeswoman for South Western Ambulance Service said.
Five others have died along British coastlines this weekend.
A mother and son, who have been named by police as Julie Walker, 37, and Lucas Walker, six, died in hospital after a rescue operation at Aberdeen beach on Saturday afternoon.
A total of five people were pulled from the water and taken to Aberdeen Royal Infirmary.
Lucas’s brother, Samuel, who bravely entered the water in an attempt to save his mother and brother, is making a “steady recovery” in hospital, police said.
A woman, in her 30s, died in hospital after getting into difficulties while swimming with a man near Green Island in Jersey on Saturday at around 8.30pm.
The man was helped to safety by members of the public, while a lifeboat managed to locate the woman who had been swept along the coast by the current, said RNLI St Helier.
She was taken to hospital but later died, Jersey Police said.
Rudy Bruynius, who has been named online, was with wife Lisinda and their daughter McKayla when they were caught up by a large wave at Fistral Beach on the north-west coast of Cornwall on Saturday.
Mr Bruynius, who is originally from South Africa but was living in London, was taken to hospital where he was pronounced dead, while McKayla was reported to be in a critical condition.
Two other children in the family managed to scramble back on to the rocks, the RNLI said.
A fundraising page, set up to support the family, has raised over £14,000.
Family friend Madelein Jansen Van Noordwyk posted a message from Lisinda which said: “Thank you all so much for your prayers!!!”
A windsurfer, in his 60s, has also died.
The man, who was rescued by RNLI lifeboats off the coast of West Mersea, Essex, at around midday on Saturday, died in hospital in Colchester.
An Essex Police spokesman said they were trying to establish the events leading up to his death.
Seven people were rescued from an angling boat off the coast of Norfolk on Sunday morning after it began to sink, the coastguard said.
The skipper called the coastguard for assistance at around 11.30am after getting into difficulties south east of Yarmouth Harbour.
Six of the seven people were taken onto waiting rescue boats while the skipper remained on board, working with Gorleston RNLI lifeboat to pump off excess water before the vessel was towed back to shore.
Jolene Smith, of the UK Coastguard, said: “This was a serious incident, but thanks to a well-trained and quick-thinking skipper and the correct communications and lifesaving equipment, we were able to ensure that rescue resources were quickly at the scene.”
The swimmer who died in hospital after getting into difficulty off Green Island in Jersey on Saturday evening has been named as Joy Godfray. It was the day before her 32nd birthday. The States of Jersey Police said her family, who do not wish to speak about the death, want to pass their “heartfelt thanks to the members of the public and all the emergency services who fought to save the life of their daughter”.