A woman was saved from drowning in the sea near Hove Lagoon by her boyfriend.
The man managed to drag her from the water after she got into difficulties.
Paramedics spent more than 20 minutes trying to resuscitate her spending ages doing CPR.
“Eventually they wrapped her in a foil sheet and took her away.
“There were a few people around but it wasn’t as busy as the beaches in the city centre and it’s not really the sort of place you would go for a swim.”
A spokesman for South East Coast Ambulance Service said: “We were called just before 4.30pm on Sunday, to Basin Road South at Shoreham Harbour, to reports of a woman who had been pulled out of the water.
“She had already been pulled out of the water when we arrived.
“The crews worked together to resuscitate the woman but she was then taken in a serious condition to the Royal Sussex County Hospital for further treatment. She was still in a serious condition on route to hospital.”
A spokesman for Sussex Police said: “A woman was pulled from the sea by her boyfriend in Basin Road South, Portslade.
“Paramedics carried out CPR on the 35-year-old woman and she was taken to Royal Sussex County Hospital.”
Brighton and Hove City Council currently employs lifeguards to man seven posts on the beach between Kemp Town and the King Alfred.
During the school holidays lifeguards will also patrol an extra three posts in the beaches in Ovingdean, Rottingdean, Saltdean and just east of Hove Lagoon.
A spokeswoman for Brighton and Hove City Council warned swimmers: “Although the weather is warming up the sea temperature is still cold.
“Those taking a dip should take care not to get out of their depth and experienced swimmers should keep to the bathing areas and wear a wetsuit.
“It’s also a good idea to swim in pairs or have someone watch from shore.”
Red and yellow flags are flown on areas of the beach patrolled by life guards when conditions are calm. Red flags mean it is unsafe to swim in the sea.