The Civil Protection Department rescued 13 teenagers late on Sunday afternoon, one of whom injured his back after jumping into the sea off a high wall.
The CPD sent two dinghies to an area close to Manoel Island, having been told that there was a person in difficulty.
The injured person, a 16-year-old, was rescued and rushed to Mater Dei Hospital in an ambulance, while another 12 teenagers aged 12 to 16 were taken back to the quay after they too encountered difficulties in the sea.