The ambulance service was called to a teenager who dived headfirst into shallow water off the eastern harbour arm in Southwick yesterday.
Tony Parker, director of engineering at Shoreham Port, said a teenage boy, who was with a group of others, had dived into the sea at around 3.30pm yesterday (Wednesday, August 8).
He said: “Unfortunately, the water there was only four foot deep and he hit the bottom.
“Fortunately a surfer nearby spotted what had happened and pulled the boy to his surfboard and took him to the beach.”
An ambulance was called to the scene.
Mr Parker said: “It wasn’t easy getting the boy off the beach and three of our lads helped the three paramedics lift him.”
An ambulance spokesman confirmed one ambulance and one car were sent to reports of a person with a head injury.
The patient was treated at the scene before being taken to Royal Sussex County Hospital in Brighton, the spokesman said.
Mr Parker warned anyone jumping into the sea in this area to check the depth of the water first.
He said: “The water depth varies with the tide – the depth one day might be three metres but the next it might be low.
“We would rather people didn’t jump off it at all but if you do, please check the depth of the water.”