On Sunday afternoon volunteers from the city’s RNLI lifeboat team were called to save a 13-year-old boy.
The youngster had become trapped by rising tide water on the outfall pier at Langstone Harbour after being abandoned by his friends.
Unable to swim to safety, the topless teen was left to wait for an hour until a fisherman eventually raised the alarm.
Aaron Gent, of the RNLI, was one of those scrambled to save the boy.
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It comes after six people across the UK died in the sea over the weekend.
Mr Gent said: ‘He didn’t want to swim back because of the fast-flowing tidal waters.
‘He was very lucky to have been spotted.’
Mr Gent is now warning people about the ‘horrendous dangers’ of the city’s coast.
He said: ‘It’s all the hidden dangers of the sea. We can get horrible, fast-flowing waters and riptides – sometimes between six and eight knots.
‘Even an Olympic swimmer can’t swim against a riptide.’
Other advice includes using lifeguard-run beaches, letting someone know what time you will be home and checking the weather before sailing or swimming.